Phase Ia/b Study of Giredestrant ± Palbociclib and ± Luteinizing Hormone-Releasing Hormone Agonists in Estrogen Receptor-Positive, HER2-Negative, Locally Advanced/Metastatic Breast Cancer

PURPOSE

Giredestrant is an investigational next-generation, oral, selective estrogen receptor antagonist and degrader for the treatment of estrogen receptor-positive (ER+) breast cancer. We present the primary analysis results of the phase Ia/b GO39932 study (NCT03332797).

PATIENTS AND METHODS

Patients with ER+, HER2-negative locally advanced/metastatic breast cancer previously treated with endocrine therapy received single-agent giredestrant (10, 30, 90, or 250 mg), or giredestrant (100 mg) ± palbociclib 125 mg ± luteinizing hormone-releasing hormone (LHRH) agonist. Detailed cardiovascular assessment was conducted with giredestrant 100 mg. Endpoints included safety (primary), pharmacokinetics, pharmacodynamics, and efficacy.

RESULTS

As of January 28, 2021, with 175 patients enrolled, no dose-limiting toxicity was observed, and the MTD was not reached. Adverse events (AE) related to giredestrant occurred in 64.9% and 59.4% of patients in the single-agent ± LHRH agonist and giredestrant + palbociclib ± LHRH agonist cohorts, respectively (giredestrant-only-related grade 3/4 AEs were reported in 4.5% of patients across the single-agent cohorts and 3.1% of those with giredestrant + palbociclib). Dose-dependent asymptomatic bradycardia was observed, but no clinically significant changes in cardiac-related outcomes: heart rate, blood pressure, or exercise duration. Clinical benefit was observed in all cohorts (48.6% of patients in the single-agent cohort and 81.3% in the giredestrant + palbociclib ± LHRH agonist cohort), with no clear dose relationship, including in patients with ESR1-mutated tumors.

CONCLUSIONS

Giredestrant was well tolerated and clinically active in patients who progressed on prior endocrine therapy. Results warrant further evaluation of giredestrant in randomized trials in early- and late-stage ER+ breast cancer.

SEOM-GEICAM-SOLTI clinical guidelines in advanced breast cancer (2022)

Advanced breast cancer represents a challenge for patients and for physicians due its dynamic genomic changes yielding to a resistance to treatments. The main goal is to improve quality of live and survival of the patients through the most appropriate subsequent therapies based on the knowledge of the natural history of the disease. In these guidelines, we summarize current evidence and available therapies for the medical management of advanced breast cancer.

Genomic characterisation of hormone receptor-positive breast cancer arising in very young women

BACKGROUND

Very young premenopausal women diagnosed with hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+HER2-) early breast cancer (EBC) have higher rates of recurrence and death for reasons that remain largely unexplained.

PATIENTS AND METHODS

Genomic sequencing was applied to HR+HER2- tumours from patients enrolled in the Suppression of Ovarian Function Trial (SOFT) to determine genomic drivers that are enriched in young premenopausal women. Genomic alterations were characterised using next-generation sequencing from a subset of 1276 patients (deep targeted sequencing, n = 1258; whole-exome sequencing in a young-age, case-control subsample, n = 82). We defined copy number (CN) subgroups and assessed for features suggestive of homologous recombination deficiency (HRD). Genomic alteration frequencies were compared between young premenopausal women (<40 years) and older premenopausal women (≥40 years), and assessed for associations with distant recurrence-free interval (DRFI) and overall survival (OS).

RESULTS

Younger women (<40 years, n = 359) compared with older women (≥40 years, n = 917) had significantly higher frequencies of mutations in GATA3 (19% versus 16%) and CN amplifications (CNAs) (47% versus 26%), but significantly lower frequencies of mutations in PIK3CA (32% versus 47%), CDH1 (3% versus 9%), and MAP3K1 (7% versus 12%). Additionally, they had significantly higher frequencies of features suggestive of HRD (27% versus 21%) and a higher proportion of PIK3CA mutations with concurrent CNAs (23% versus 11%). Genomic features suggestive of HRD, PIK3CA mutations with CNAs, and CNAs were associated with significantly worse DRFI and OS compared with those without these features. These poor prognostic features were enriched in younger patients: present in 72% of patients aged <35 years, 54% aged 35-39 years, and 40% aged ≥40 years. Poor prognostic features [n = 584 (46%)] versus none [n = 692 (54%)] had an 8-year DRFI of 84% versus 94% and OS of 88% versus 96%. Younger women (<40 years) had the poorest outcomes: 8-year DRFI 74% versus 85% and OS 80% versus 93%, respectively.

CONCLUSION

These results provide insights into genomic alterations that are enriched in young women with HR+HER2- EBC, provide rationale for genomic subgrouping, and highlight priority molecular targets for future clinical trials.

Adjuvant Endocrine Therapy in Premenopausal Breast Cancer: 12-Year Results From SOFT

Clinical trials frequently include multiple end points that mature at different times. The initial report, typically based on the primary end point, may be published when key planned co-primary or secondary analyses are not yet available. Clinical Trial Updates provide an opportunity to disseminate additional results from studies, published in JCO or elsewhere, for which the primary end point has already been reported.The Suppression of Ovarian Function Trial (SOFT; ClinicalTrials.gov identifier: NCT00066690) randomly assigned premenopausal women with hormone receptor-positive breast cancer to 5 years of adjuvant tamoxifen, tamoxifen plus ovarian function suppression (OFS), or exemestane plus OFS. The primary analysis compared disease-free survival (DFS) between tamoxifen plus OFS versus tamoxifen alone; exemestane plus OFS versus tamoxifen was a secondary objective. After 8 years, SOFT reported a significant reduction in recurrence and improved overall survival (OS) with adjuvant tamoxifen plus OFS versus tamoxifen alone. Here, we report outcomes after median follow-up of 12 years. DFS remained significantly improved with tamoxifen plus OFS versus tamoxifen (hazard ratio, 0.82; 95% CI, 0.69 to 0.98) with a 12-year DFS of 71.9% with tamoxifen, 76.1% with tamoxifen plus OFS, and 79.0% with exemestane plus OFS. OS was improved with tamoxifen plus OFS versus tamoxifen (hazard ratio, 0.78; 95% CI, 0.60 to 1.01) and was 86.8% with tamoxifen, 89.0% with tamoxifen plus OFS, and 89.4% with exemestane plus OFS at 12 years. Among those who received prior chemotherapy for human epidermal growth factor receptor-2-negative tumors, OS was 78.8% with tamoxifen, 81.1% with tamoxifen plus OFS, and 84.4% with exemestane plus OFS. In conclusion, after 12 years, there remains a benefit from including OFS in adjuvant endocrine therapy, with an absolute improvement in OS more apparent with higher baseline risk of recurrence.[Media: see text].

Palbociclib Rechallenge for Hormone Receptor-Positive/HER-Negative Advanced Breast Cancer: Findings from the Phase II BioPER Trial

PURPOSE

To assess the efficacy and exploratory biomarkers of continuing palbociclib plus endocrine therapy (ET) beyond progression on prior palbociclib-based regimen in patients with hormone receptor-positive/HER2-negative (HR+/HER2-) advanced breast cancer (ABC).

PATIENTS AND METHODS

The multicenter, open-label, phase II BioPER trial included women who had experienced a progressive disease (PD) after having achieved clinical benefit on the immediately prior palbociclib plus ET regimen. Palbociclib (125 mg, 100 mg, or 75 mg daily orally for 3 weeks and 1 week off as per prior palbociclib-based regimen) plus ET of physician's choice were administered in 4-week cycles until PD or unacceptable toxicity. Coprimary endpoints were clinical benefit rate (CBR) and percentage of tumors with baseline loss of retinoblastoma (Rb) protein expression. Additional endpoints included safety and biomarker analysis.

RESULTS

Among 33 patients enrolled, CBR was 34.4% [95% confidence interval (CI), 18.6-53.2; P < 0.001] and 13.0% of tumors (95% CI, 5.2-27.5) showed loss of Rb protein expression, meeting both coprimary endpoints. Median progression-free survival was 2.6 months (95% CI, 1.8-6.7). No new safety signals were reported. A signature that included baseline mediators of therapeutic resistance to palbociclib and ET (low Rb score, high cyclin E1 score, ESR1 mutation) was independently associated with shorter median progression-free survival (HR, 22.0; 95% CI, 1.71-282.9; P = 0.018).

CONCLUSIONS

Maintaining palbociclib after progression on prior palbociclib-based regimen seems to be a reasonable, investigational approach for selected patients. A composite biomarker signature predicts a subset of patients who may not derive a greater benefit from palbociclib rechallenge, warranting further validation in larger randomized controlled trials.

The oral selective estrogen receptor degrader GDC-0810 (ARN-810) in postmenopausal women with hormone receptor-positive HER2-negative (HR + /HER2 -) advanced/metastatic breast cancer

PURPOSE

GDC-0810 (ARN-810) is a novel, non-steroidal, orally bioavailable, selective estrogen receptor degrader (SERD) that potentially inhibits ligand-dependent and ligand-independent estrogen receptor (ER)-mediated signaling.

METHODS

A phase Ia/Ib/IIa dose escalation, combination treatment with palbociclib or a luteinizing hormone-releasing hormone, and expansion study determined the safety, pharmacokinetics, and recommended phase 2 dose (RP2D) of GDC-0810 in postmenopausal women with ER + (HER2 -) locally advanced or metastatic breast cancer (MBC). Baseline plasma ctDNA samples were analyzed to determine the ESR1 mutation status.

RESULTS

Patients (N = 152) received GDC-0810 100-800 mg once daily (QD) or 300-400 mg twice daily, in dose escalation, expansion, as single agent or combination treatment. Common adverse events regardless of attribution to study drug were diarrhea, nausea, fatigue, vomiting, and constipation. There was one dose-limiting toxicity during dose escalation. The maximum tolerated dose was not reached. GDC-0810 600 mg QD taken with food was the RP2D. Pharmacokinetics were predictable. FES reduction (> 90%) highlighting pharmacodynamic engagement of ER was observed. Outcomes for the overall population and for patients with tumors harboring ESR1 mutations included partial responses (4% overall; 4% ESR1), stable disease (39% overall; 42% ESR1), non-complete response/non-progressive disease (13% overall; 12% ESR1), progressive disease (40% overall; 38% ESR1), and missing/unevaluable (5% overall; 5% ESR1). Clinical benefit (responses or SD, lasting ≥ 24 weeks) was observed in patients in dose escalation (n = 16, 39%) and expansion (n = 24, 22%).

CONCLUSION

GDC-0810 was safe and tolerable with preliminary anti-tumor activity in heavily pretreated patients with ER + advanced/MBC, with/without ESR1 mutations, highlighting the potential for oral SERDs. Clinical Trial and registration date April 4, 2013. NCT01823835 .

Palbociclib with Fulvestrant or Letrozole in Endocrine-Sensitive Patients with HR-Positive/HER2-Negative Advanced Breast Cancer: A Detailed Safety Analysis of the Randomized PARSIFAL Trial

BACKGROUND

Palbociclib has gained a central role in the treatment of hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC). Despite its manageable toxicity profile, venous thromboembolism (VTE) or interstitial lung disease (ILD)/pneumonitis may infrequently occur. Therefore, we provide a comprehensive summary of the safety and tolerability of the combination of endocrine therapy and palbociclib among patients included in the randomized phase 2 PARSIFAL study.

MATERIALS AND METHODS

Patients with endocrine-sensitive HR+/HER2- ABC and no prior therapy in an advanced setting (n = 486) were randomly assigned 1:1 to receive fulvestrant-palbociclib (FP) or letrozole-palbociclib (LP). Laboratory tests and the incidence of adverse events (AEs) were recorded at baseline and day 1 of each cycle. Progression-free survival (PFS) was estimated for patients with and without VTE.

RESULTS

A total of 483 patients were analyzed. Neutropenia, leukopenia, anemia, asthenia, arthralgia, fatigue, and diarrhea were the most frequent AEs in both groups. Febrile neutropenia occurred in 3 (1.2%) patients of the FP group and in 1 (0.4%) patient in the LP group. Six (2.5%; 0.4% grade 3) patients in the FP group and 6 patients (2.5%; 0.4% grade 3) in the LP group experienced ILD/pneumonitis. Pulmonary embolism was reported in 12 (5.0%) patients in the FP group and 6 (2.5%) patients in the LP group. Advanced age at baseline was the only factor significantly associated with an increased risk of pulmonary embolism (P < .01).

CONCLUSION

The PARSIFAL data confirmed the favorable safety profile of both palbociclib regimens. VTE and ILD/pneumonitis were occasionally reported, and their early detection allowed patients to continue treatment effectively without detriment to efficacy.

CLINICALTRIALS.GOV IDENTIFIER

NCT02491983; https://clinicaltrials.gov/ct2/show/NCT02491983).

Giredestrant reverses progesterone hypersensitivity driven by estrogen receptor mutations in breast cancer

ESR1 (estrogen receptor 1) hotspot mutations are major contributors to therapeutic resistance in estrogen receptor-positive (ER⁺) breast cancer. Such mutations confer estrogen independence to ERα, providing a selective advantage in the presence of estrogen-depleting aromatase inhibitors. In addition, ESR1 mutations reduce the potency of tamoxifen and fulvestrant, therapies that bind ERα directly. These limitations, together with additional liabilities, inspired the development of the next generation of ERα-targeted therapeutics, of which giredestrant is a high-potential candidate. Here, we generated Esr1 mutant-expressing mammary gland models and leveraged patient-derived xenografts (PDXs) to investigate the biological properties of the ESR1 mutations and their sensitivity to giredestrant in vivo. In the mouse mammary gland, Esr1 mutations promote hypersensitivity to progesterone, triggering pregnancy-like tissue remodeling and profoundly elevated proliferation. These effects were driven by an altered progesterone transcriptional response and underpinned by gained sites of ERα-PR (progesterone receptor) cobinding at the promoter regions of pro-proliferation genes. PDX experiments showed that the mutant ERα-PR proliferative program is also relevant in human cancer cells. Giredestrant suppressed the mutant ERα-PR proliferation in the mammary gland more so than the standard-of-care agents, tamoxifen and fulvestrant. Giredestrant was also efficacious against the progesterone-stimulated growth of ESR1 mutant PDX models. In addition, giredestrant demonstrated activity against a molecularly characterized ESR1 mutant tumor from a patient enrolled in a phase 1 clinical trial. Together, these data suggest that mutant ERα can collaborate with PR to drive protumorigenic proliferation but remain sensitive to inhibition by giredestrant.

High p16 expression and heterozygous RB1 loss are biomarkers for CDK4/6 inhibitor resistance in ER+ breast cancer

CDK4/6 inhibitors combined with endocrine therapy have demonstrated higher antitumor activity than endocrine therapy alone for the treatment of advanced estrogen receptor-positive breast cancer. Some of these tumors are de novo resistant to CDK4/6 inhibitors and others develop acquired resistance. Here, we show that p16 overexpression is associated with reduced antitumor activity of CDK4/6 inhibitors in patient-derived xenografts (n = 37) and estrogen receptor-positive breast cancer cell lines, as well as reduced response of early and advanced breast cancer patients to CDK4/6 inhibitors (n = 89). We also identified heterozygous RB1 loss as biomarker of acquired resistance and poor clinical outcome. Combination of the CDK4/6 inhibitor ribociclib with the PI3K inhibitor alpelisib showed antitumor activity in estrogen receptor-positive non-basal-like breast cancer patient-derived xenografts, independently of PIK3CA, ESR1 or RB1 mutation, also in drug de-escalation experiments or omitting endocrine therapy. Our results offer insights into predicting primary/acquired resistance to CDK4/6 inhibitors and post-progression therapeutic strategies.

Utility of liquid biopsy for identifying emerging mutations (mut) and novel treatment options in luminal metastatic breast cancer (LMBC)

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Background: Molecular characterization of LMBC for the choice of therapy and inclusion in clinical trials is frequently performed in archival biopsies procured several years before. Emerging mut secondary to therapeutic pressure are hence frequently missed but could be detected by real-time analysis of circulating tumor DNA. Aim: 1) To assess the emergence of ERBB2 and other mut upon therapeutic pressure; 2) To compare the concordance of mut in tumor and plasma samples between patients (pts) with metachronous and synchronous sample acquisition. Methods: Pts with LMBC and available tumor biopsy and plasma samples were identified and divided in two groups: 1) Cohort 1 (metachronous) if the time between tissue and plasma acquisition was > 3 months and systemic treatment was given between the sampling; 2) Cohort 2 (synchronous) if sampling occurred with < 3 months interval in the absence of systemic treatment. Tumor and plasma were analyzed using MiSeq Amplicon-based NGS (custom panel of 60 cancer-related genes). The emergent mut in plasma in Cohort 1 and the concordance of ESCAT Tier I and II mut ( PIK3CA, AKT1, ERBB2, ESR1, PTEN) in both Cohorts were determined and correlated with clinical features. Results: 176 pts were included, 112 in Cohort 1 and 64 in Cohort 2. In Cohort 1, emerging mut in PIK3CA were identified in 5 cases (14% of total cases with PIK3CA mut), ESR1 in 22 cases (85% of cases with ESR1 mut) and PTEN in 3 cases (43% of cases with PTEN mut). No emerging ERBB2 or AKT1 mut were seen in plasma. In Cohort 1 ERBB2 mut were identified in 10 pts (8.9%), 5 both in plasma and tissue and 5 only in tissue. Concordance between tumor and plasma was 53% in Cohort 1 and 66% in Cohort 2 (95% CI of the difference -2% to 38%, P =.09). In Cohort 1, concordance was not associated with (neo)adjuvant treatment, number of lines for MBC, presence of visceral metastasis, location of biopsy (primary tumor or metastasis), interval between sampling (range 3.6 – 288 months) or type of systemic treatment before plasma sampling. In Cohort 2, higher concordance associated with shorter interval between primary diagnosis and sampling (p = 0.02). PI3KCA and ESR1 were the two genes most frequently altered in both cohorts. PI3KCA mut had the highest degree of concordance in both groups (70% in Cohort 1 and 76% in Cohort 2). Concordance for ESR1 mut was low in both cohorts (20% and 48%, respectively). Conclusions: A significant number of ESR1 mut emerged upon therapeutic pressure in LMBC. Plasma analysis could also detect the emergence of PIK3CA and PTEN, but not ERBB2 mut. The trend towards lower concordance between metachronous and synchronous tumor and plasma sampling is probably due to increased tumor heterogeneity and clonal diversity secondary to systemic treatment. Our findings confirm that liquid biopsies provide complementary information respect to tumor tissue that may be potentially useful for clinical decisions.

Preclinical In Vivo Validation of the RAD51 Test for Identification of Homologous Recombination-Deficient Tumors and Patient Stratification

PARP inhibitors (PARPi) are approved drugs for platinum-sensitive, high-grade serous ovarian cancer (HGSOC) and for breast, prostate, and pancreatic cancers (PaC) harboring genetic alterations impairing homologous recombination repair (HRR). Detection of nuclear RAD51 foci in tumor cells is a marker of HRR functionality, and we previously established a test to detect RAD51 nuclear foci. Here, we aimed to validate the RAD51 score cut off and compare the performance of this test to other HRR deficiency (HRD) detection methods. Laboratory models from BRCA1/BRCA2-associated breast cancer, HGSOC, and PaC were developed and evaluated for their response to PARPi and cisplatin. HRD in these models and patient samples was evaluated by DNA sequencing of HRR genes, genomic HRD tests, and RAD51 foci detection. We established patient-derived xenograft models from breast cancer (n = 103), HGSOC (n = 4), and PaC (n = 2) that recapitulated patient HRD status and treatment response. The RAD51 test showed higher accuracy than HRR gene mutations and genomic HRD analysis for predicting PARPi response (95%, 67%, and 71%, respectively). RAD51 detection captured dynamic changes in HRR status upon acquisition of PARPi resistance. The accuracy of the RAD51 test was similar to HRR gene mutations for predicting platinum response. The predefined RAD51 score cut off was validated, and the high predictive value of the RAD51 test in preclinical models was confirmed. These results collectively support pursuing clinical assessment of the RAD51 test in patient samples from randomized trials testing PARPi or platinum-based therapies.

SIGNIFICANCE

This work demonstrates the high accuracy of a histopathology-based test based on the detection of RAD51 nuclear foci in predicting response to PARPi and cisplatin.

Abstract P1-07-02: Primary results of ONAWA (SOLTI-1802) trial: A window of opportunity trial of onapristone in postmenopausal women with progesterone receptor-positive/HER2-negative early breast cancer (EBC)

Background PgR expression is a biomarker of ER functionality, cellular progression to malignancy, and response to endocrine therapy (ET) in HR+ BC. Onapristone (ONA), a type 1 antiprogestin, was shown to have a single agent anti-tumor activity in patients with metastatic breast cancer (Robertson et al., 1999; Jonat et al., 2002). However, this once daily immediate-release formulation was associated with liver function test abnormalities in one-third of patients. A new, extended-release formulation (ONA XR) was developed and was evaluated in a BID schedule that reduced peak serum concentrations while sustaining the minimum plasma concentrations previously associated with the higher dose. Safety results of two phase I-II studies confirmed this hypothesis (Cottu et al., 2018; Jayaram et al., 2017; Lewis et al, 2020). Considering BC heterogeneity and that PgR analysis by standard immunohistochemistry (IHC) does not perfectly correlate with PgR target gene expression, the identification of biomarkers allowing the selection of patients with PgR-driven tumors that may benefit from antiprogestins treatment is currently an unmet need. Patients and Methods ONAWA (NCT04142892) is an open-label, single-arm, multicenter window of opportunity clinical trial of ONA XR (50 mg BID for 21 days) for postmenopausal women with EBC amenable to receive a short course of ET before surgery. Ten patients with ER+/PgR+/HER2- and Ki-67 ≥ 15% BC were enrolled. The primary objective is to evaluate the biological activity of ONA by the rate of Complete Cell Cycle Arrest (CCCR) determined by Ki-67 (≤2.7%). Secondary endpoints include safety and correlating biological activity with IHC of tumor expression (ER, PgR, Ser294-PgR, CD24, CD44, ALDH1, Ki-67), estradiol, and progesterone blood levels, and gene expression profile (NanoString nCounter® Breast 360TM panel). Relative Ki-67 suppression was defined as (1 - Ln(Ki-67 Baseline)/Ln(Ki-67 surgery)) Results Assessment of the treatment effects was possible for the 10 patients who successfully completed the protocol and the 10 paired samples (100%) were analyzed. Main patient characteristics were mean age 68 (range 53-81 years), mean tumor size 20.2 mm (range 15-26 mm), stage I (40%) and grade 2 (100%). No patients achieved a CCCR. Tumor Ki-67 expression decreased in six patients was stable in one patient and increased three patients. The mean percentage suppression of Ki-67 was 19.58%. Overall, no statistically significant change was observed in Ki-67 between paired samples (p=0.234). Baseline IHC PgR (%) expression correlated with Ki-67 decrease (r = -0.635). Mean percentage suppression of Ki-67 for tumors with IHC PgR expression ≥90% (N=4) and &lt;90% (N=6) was -25.23.0% and +2.54%, respectively. Six (60%) patients reported AEs at any grade. Most common grade 1 or 2 AEs were post-procedural pain, dry mouth and GGT increased. Grade 3 reversible GGT and AST increase occurred in 1 patient. Conclusion: ONA XR significantly increases suppression of tumor cell proliferation in PgR-high primary breast cancer. The safety profile was consistent with that previously reported. Additional correlative analysis including gene expression will be presented. Acknowledgments: Funding and drug provided by Context Therapeutics Inc., USA.

Citation Format: Meritxell Bellet, Serafin Morales, Ariadna Gasol, Kepa Amillano, Nuria Chic, Xavier González-Farré, Patricia Villagrasa, Laia Paré, Claudette Falato, Paolo Nuciforo, Débora Martínez, Juan M Ferrero-Cafiero, Tomás Pascual, Aleix Prat, Carol Lange, Cristina Saura. Primary results of ONAWA (SOLTI-1802) trial: A window of opportunity trial of onapristone in postmenopausal women with progesterone receptor-positive/HER2-negative early breast cancer (EBC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-07-02.

Abstract P5-18-07: Heart rate changes, cardiac safety, and exercise tolerance from a phase Ia/b study of giredestrant (GDC-9545) ± palbociclib in patients with estrogen receptor-positive, HER2-negative locally advanced/metastatic breast cancer

Background Targeting the activity of the estrogen receptor and/or estrogen synthesis is a standard primary treatment for eligible patients with estrogen receptor-positive breast cancer. Giredestrant is a highly potent, nonsteroidal oral selective estrogen receptor antagonist and degrader that achieves robust estrogen receptor occupancy. In animal models and early phase studies, giredestrant was associated with a dose-dependent reduction in heart rate. Therefore, we leveraged an ongoing nonrandomized, open-label, dose-escalation and -expansion phase Ia/b study (GO39932) to evaluate its cardiac safety. Methods Eligibility criteria for the main study are available at https://clinicaltrials.gov/ct2/show/NCT03332797. Additional relevant cardiac exclusion criteria included current treatment with medications known to decrease heart rate, e.g., beta blockers.100 mg giredestrant was given daily on Days 1-28 of each 28-day cycle (monotherapy for 14 days; patients then continued monotherapy or received combination treatment with 125 mg daily oral palbociclib for the study duration, per investigator decision). The 100 mg giredestrant dose for this arm (rather than the phase III 30 mg dose) was evaluated to increase the likelihood of observing relevant cardiac effects. Electrocardiograms were required on Day 1 of each cycle; 24-hour Holter data were collected and treadmill-exercise testing was completed at screening (prior to starting giredestrant), steady state (Day 8 [+3 days]), and as clinically indicated. Exercise testing evaluated baseline heart rate, exercise duration, maximal heart rate, and heart rate recovery. A standard Bruce protocol was followed. Results Clinical data cutoff was Apr 16, 2021. Twenty patients were enrolled and included in the current analysis; median age was 59 (range, 45-72); three patients (15%) had a history of hypertension at screening. During follow-up, no dysrhythmias were observed that required treatment or a change in study medication, and no patients were noted to have a resting heart rate of &lt;50 beats per minute based on routine heart rate monitoring. Two Grade 1 bradycardia events (&lt;60 beats per minute) were reported; both in patients receiving palbociclib. No other cardiac adverse events (AEs) were reported overall, nor any other serious AEs. Holter monitoring reports were available for 19 patients at screening and 20 on treatment. There were no episodes of second- or third-degree atrioventricular block. At screening, 2/19 patients (11%) had a paroxysmal supraventricular tachycardia event (SVT; ≤30 seconds). During the study, 4/20 patients (20%) had a paroxysmal SVT event and, of these, 1/4 had four episodes of an SVT event lasting &gt;30 seconds and 1/4 also experienced one episode of non-sustained ventricular tachycardia. No patients required any cardiac treatment or dose modification. Twenty patients underwent exercise testing. Exercise time was similar among patients before and after starting giredestrant (mean exercise time 7 min 10 sec before; 7 min 44 sec after). Exercise intensity was similar before and after starting treatment (mean metabolic equivalents expenditure 7.52 [standard deviation 2.81] and 8.68 [2.78], respectively). One patient had an abnormal heart rate recovery on exercise testing at screening and again while on treatment. Conclusions In a thorough cardiac safety analysis, applying routine electrocardiograms, 24-hour Holter monitoring, and exercise testing, no clinically relevant cardiac effects were observed with 100 mg giredestrant (a higher dose than the phase III 30 mg dose).

Citation Format: Tomas G Neilan, Rafael Villanueva-Vázquez, Meritxell Bellet, Elena López-Miranda, Laura García-Estévez, Peter Kabos, John Bond, Mary R Gates, Ching-Wei Chang, Valentina Boni. Heart rate changes, cardiac safety, and exercise tolerance from a phase Ia/b study of giredestrant (GDC-9545) ± palbociclib in patients with estrogen receptor-positive, HER2-negative locally advanced/metastatic breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-18-07.

Abstract OT2-11-07: Solti-1905. Elacestrant in preoperative setting, a window of opportunity study (ELIPSE trial)

Background.Patients with hormone receptor-positive/HER2-negative (HR+/HER2-) breast cancer (BC) are mainly treated with therapies that target estrogen receptor (ER) signaling to impair tumor cell proliferation. Several drugs targeting the ER pathway are currently used in the clinical practice including aromatase inhibitors (AI) that limit the production of estradiol, selective ER modulators (SERMs) that compete with estradiol for binding ER, and selective ER degraders (SERDs) that induce ER degradation. Despite the availability of these drugs, finding new ET remains a clinical unmet need since some patients do not initially respond to these treatments or become resistant to available endocrine agents. Elacestrant is an orally bioavailable drug that acts as SERD in breast tissue promoting degradation of ER and inhibiting breast cancer cell proliferation. Several clinical studies have confirmed the tolerable safety profile of elacestrant in BC (Bardia A et al. ASCO, 2021) and a phase III trial investigating elacestrant versus standard ET in metastatic BC patients is ongoing for patients treated with at least 1 prior ET and a CDK4/6 inhibitor for advanced BC (EMERALD; NCT03778931). In this study, we aim to investigate the biological effect of elacestrant on cell proliferation in patients with ER+/HER2- resectable BC. Study design. ELIPSE is prospective, multicenter, single-arm, window-of-opportunity study designed to evaluate the biological effect of elacestrant in treatment naïve patients with ER+/HER2- resectable BC. The study population consists of postmenopausal women with clinically negative axillary lymph node (cN0) and whose primary tumors are≥ 1.5 cm by ultrasound with Ki67 ≥10% locally assessed. Patients will receive 400 mg of elacestrant in monotherapy orally, once a day, continuously. After 4 weeks of treatment, surgery will be performed in accordance with local practice. Two biopsies of the same lesion will be obtained as mandatory: a baseline sample and a surgical sample (tumor core-biopsy is permitted if surgery is not performed after 4 weeks of treatment). Plasma samples for biomarkers will be collected at baseline, surgery and end of study visit. The primary objective is to evaluate the Complete Cell Cycle Arrest rate (defined as Ki67 ≤ 2.7%) by central assessment after 4 weeks of elacestrant therapy. Secondary endpoints include:. 1) safety,. 2) correlation of biological activity determined by changes in: Ki67 as a continuous variable, intrinsic PAM50 subtypes, proliferative signatures, tumor cellularity and tumor-infiltrating lymphocytes (CelTIL, Nuciforo P et al., Ann Oncol, 2018) in tumor samples taken before and at the end of treatment, and. 3) analysis of ctDNA dynamics after treatment. As of July 2021, 7 patients have been enrolled in 4 sites in Spain. NCT04797728. Acknowledgement. This study is financially supported by Radius Pharmaceuticals, Inc.

Citation Format: María Vidal, Montserrat Muñoz, Mireia Margeli, Xavier González, Kepa Amillano, Rodrigo Sánchez-Bayona, Fernando Salvador, Tomás Pascual, Aleix Prat, Meritxell Bellet. Solti-1905. Elacestrant in preoperative setting, a window of opportunity study (ELIPSE trial) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-11-07.

Abstract OT2-06-01: Solti-1903 HOPE: Real-world clinical practice study to assess the impact of using genomic data on the next treatment decision making-choice in patients with locally advanced or metastatic breast cancer in Spain

BACKGROUND: Metastatic breast cancer (mBC) remains an incurable disease and is the cause of nearly all deaths related to BC. Next-generation sequencing technologies are allowing the application of personalized targeted molecular therapies, thereby improving outcomes in breast cancer patients. However, they are not routinely used in the clinic and their cost could be a cause of disparity. One strategy to overcome the barriers of implementing NGS in the clinic is to promote the active participation of patients with mBC in the management of their disease and offering free access to these tests. With this in mind, we designed HOPE (SOLTI-1903), a Spanish real-world study where patients lead their inclusion, participation, and follow-up through a digital tool (DT) that guides them in every step of the journey. The ultimate objective of HOPE is to gather real-world data on the utilization of molecular information in the management of mBC and to empower these patients. TRIAL DESIGN: Patients diagnosed with locally advanced or mBC can be included. Basic demographic data, disease characteristics, treatment history and quality of life data are collected by patients through a DT. The study is complemented by a patient empowerment program including informative workshops and precision medicine video-tutorials. Patients are encouraged to involve their physicians in HOPE. A total of 600 patients will be included in Spain. PATIENT JOURNEY: Once patients request participation through the DT, a dedicated team in SOLTI assists them in the subsequent steps while validating that eligibility criteria are met according to patient-provided data. Then, patients receive instructions from SOLTI’s team to attend the nearest partner local laboratory, where they sign the study informed consent form. A metastatic (preferably) or primary archival tumor sample is requested from the patient’s reference hospital and analyzed by FoundationOne®CDx. Patients that are in progression or not receiving active systemic chemo- or radiotherapy undergo a blood draw to receive a Guardant360 analysis. These two NGS tests are offered to all patients, and the blood test is performed even if no tissue is available. The results from the molecular analyses are regularly reviewed by a Molecular Advisory Board (MAB). The MAB, based on its joint experience in clinical oncology, genomics, bioethics, and pathology, may add some advice to these reports via DT, making comments about detected molecular alterations and adding further recommendations for specific treatment options or available CT with targeted therapies and/or additional genetic tests such as germline validation of potentially significant findings. From that moment, patients are requested to record their disease evolution in the DT every 3 months for 2 years. The primary objective is to assess the real-world clinical practice integrating molecular profiling in the Standard of Care management of patients with mBC connected through a DT. Secondary objectives include to i) describe the genetic mutational profile of mBC, ii) estimate the enrollment rate in CT of patients engaged in a patient-centered strategy for molecular tumor assessment, iii) assessing Progression Free Survival, Overall Survival and Quality of Life status among patients enrolled in CT according to the tumor’s genomic profile and iv) evaluate the logistic feasibility of the study. Recruitment started on October 2020. By June 2021, 362 patients had been enrolled. ACKNOWLEDGEMENTS: This study is sponsored by SOLTI and financially supported by Novartis and three non-profit organizations: Asociación Cáncer de Mama Metastásico, Asociación Saray and Fundación Actitud frente al Cáncer. Roche and Guardant Health provide their tests for all patients.

Citation Format: Ana Casas, Eva Ciruelos, Mafalda Oliveira, Cristina Saura, Meritxell Bellet, Sonia Pernas, Joaquín Gavilá, Montserrat Muñoz, Maria Vidal, Blanca González-Farré, Juan M. Cejalvo, Rafael López, Ana Vivancos, Marcos Malumbres, Javier Salvador Bofill, Isabel Blancas, Emilio Alba, Valentina Boni, Susana De la Cruz, Elena Galve, Antonia Perelló, Mireia Margelí, Meritxell Soler, Rubén Olivera-Salguero, Helena Masanas, Rosa Olmos, Marga Forns, Pilar Fernández Pascual, Elia Seguí, Tomas Pascual, Aleix Prat. Solti-1903 HOPE: Real-world clinical practice study to assess the impact of using genomic data on the next treatment decision making-choice in patients with locally advanced or metastatic breast cancer in Spain [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-06-01.

Adjuvant Palbociclib for Early Breast Cancer: The PALLAS Trial Results (ABCSG-42/AFT-05/BIG-14-03)

PURPOSE

Palbociclib is a cyclin-dependent kinase 4 and 6 inhibitor approved for advanced breast cancer. In the adjuvant setting, the potential value of adding palbociclib to endocrine therapy for hormone receptor-positive breast cancer has not been confirmed.

PATIENTS AND METHODS

In the prospective, randomized, phase III PALLAS trial, patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative early breast cancer were randomly assigned to receive 2 years of palbociclib (125 mg orally once daily, days 1-21 of a 28-day cycle) with adjuvant endocrine therapy or adjuvant endocrine therapy alone (for at least 5 years). The primary end point of the study was invasive disease-free survival (iDFS); secondary end points were invasive breast cancer-free survival, distant recurrence-free survival, locoregional cancer-free survival, and overall survival.

RESULTS

Among 5,796 patients enrolled at 406 centers in 21 countries worldwide over 3 years, 5,761 were included in the intention-to-treat population. At the final protocol-defined analysis, at a median follow-up of 31 months, iDFS events occurred in 253 of 2,884 (8.8%) patients who received palbociclib plus endocrine therapy and in 263 of 2,877 (9.1%) patients who received endocrine therapy alone, with similar results between the two treatment groups (iDFS at 4 years: 84.2% v 84.5%; hazard ratio, 0.96; CI, 0.81 to 1.14; P = .65). No significant differences were observed for secondary time-to-event end points, and subgroup analyses did not show any differences by subgroup. There were no new safety signals for palbociclib in this trial.

CONCLUSION

At this final analysis of the PALLAS trial, the addition of adjuvant palbociclib to standard endocrine therapy did not improve outcomes over endocrine therapy alone in patients with early hormone receptor-positive breast cancer.

Investigating the endothelin receptor antagonist aprocitentan in resistant hypertension: design and baseline characteristics of the PRECISION study

 

The endothelin (ET) system plays an important role in hypertension, especially in volume and salt-dependent forms, which are common in patients with resistant hypertension (RHT). Therapies targeting the ET system may provide a new treatment option. A Phase 2 dose-finding study demonstrated an effect of the dual ET receptor antagonist aprocitentan monotherapy on blood pressure (BP) [1].

PRECISION is a randomized, parallel-group, Phase 3 study assessing the short-term effect of 2 doses of aprocitentan (12.5 mg and 25 mg) and its long-term sustained effect on BP. Following randomization, patients entered a 4-week, double-blind (DB), placebo-controlled part, followed by aprocitentan 25 mg for 32 weeks, and a 12-week, placebo-controlled, randomized withdrawal part (Figure 1). The primary endpoint is the change in systolic BP (SBP) from randomization to week 4 and the key secondary endpoint is the change in SBP from re-randomization to week 40.

The study enrolled 1971 patients with RHT diagnosed according to the site's medical practice, from 193 centres worldwide. Entry criteria included sitting SBP [SiSBP] ≥140 mmHg, measured by unattended automated office BP (uAOBP, reducing the white coat effect), despite the use of ≥3 antihypertensive medications. During the screening period of 4 to 12 weeks, secondary causes of hypertension were excluded by the investigator and patients still having SiSBP ≥140 mmHg were switched from their individual antihypertensive drugs to a single-tablet, triple combination of valsartan 160 mg /amlodipine 5 or 10 mg /hydrochlorothiazide 25 mg o.d. (minimizing medical inertia and improving drug adherence) for at least 4 weeks before entering the placebo run-in (RI) period. The screening failure rate of 53% is indicative of the high incidence of apparent RHT within the hypertensive population.

Patients continuing having SiSBP ≥140 mmHg on triple therapy (true RHT) then entered the 4-week, single-blind placebo RI period. Of these patients, 20% failed to be randomized, most frequently because of SiSBP &lt;140 mmHg, possibly due to a placebo effect.

As of 12 March 2021, 860 patients were in the placebo RI period and 664 patients were randomized, 30% from North America, 62% from Europe, and 8% from Asia/Australia. Mean age was 61.8 years (standard deviation [SD]=10.8). 40% of patients were women, 11% were Black, 5% Asian, and 83% White. Mean body mass index (BMI) was 33.6 kg/m2 (SD=6.4) and mean estimated glomerular filtration rate (eGFR) was 76.8 mL/min/1.73 m2 (including 21% chronic kidney disease [CKD] stage 3–4 patients). Medical history included diabetes (54%), myocardial infarction (30%), stroke (23%), congestive heart failure (19%), and sleep apnoea (15%). In addition to the standardized antihypertensive medication, 59% of patients used beta-blockers. Mean baseline SiSBP/SiDBP was 153/88 mmHg. Results of the trial will be available in 2022.

Funding Acknowledgement

Type of funding sources: Private company. Main funding source(s): The PRECISION study is sponsored by Idorsia Pharmaceuticals Ltd.

Fulvestrant-Palbociclib vs Letrozole-Palbociclib as Initial Therapy for Endocrine-Sensitive, Hormone Receptor-Positive, ERBB2-Negative Advanced Breast Cancer: A Randomized Clinical Trial

Importance

The cyclin-dependent kinase 4 and 6 inhibitor palbociclib in combination with letrozole has become a standard first-line treatment for patients with endocrine-sensitive, hormone receptor-positive, ERBB2-negative advanced breast cancer. Meanwhile, the antiestrogen fulvestrant was shown to be superior to anastrozole in the absence of cyclin-dependent kinase 4 and 6 inhibition for this patient population.

Objective

To assess whether fulvestrant is superior to letrozole when combined with palbociclib in the first-line scenario.

Design, Setting, and Participants

In this international, randomized, open-label, phase 2 clinical study conducted from July 30, 2015, to January 8, 2018, patients with hormone receptor-positive, ERBB2-negative advanced breast cancer with no prior therapy in the metastatic setting and endocrine-sensitive criteria were recruited from 47 centers in 7 countries. Data were analyzed from February 11 to May 15, 2020.

Interventions

Patients were randomly assigned (1:1 ratio) to receive palbociclib with either fulvestrant or letrozole. Stratification factors were type of disease presentation (de novo vs recurrent) and the presence of visceral involvement (yes vs no).

Main Outcomes and Measures

The primary end point was investigator-assessed progression-free survival determined by Response Evaluation Criteria in Solid Tumors, version 1.1.

Results

A total of 486 women (median age, 63 years [range, 25-90 years]; 3 Asian women [0.6%]; 4 Black women [0.8%]; 461 White women [94.9%]; 18 women of unknown race [3.7%]) were randomized (243 to fulvestrant-palbociclib and 243 to letrozole-palbociclib). Median investigator-assessed progression-free survival was 27.9 months (95% CI, 24.2-33.1 months) in the fulvestrant-palbociclib group vs 32.8 months (95% CI, 25.8-35.9 months) in the letrozole-palbociclib group (hazard ratio, 1.13; 95% CI, 0.89-1.45; P = .32). This result was consistent across the stratification factors. No significant differences were observed in objective response rate (46.5% vs 50.2%) and 3-year overall survival rate (79.4% vs 77.1%) for fulvestrant-palbociclib and letrozole-palbociclib, respectively. Grade 3-4 adverse events were comparable among treatment groups, and no new safety signals were identified. No treatment-related deaths were reported.

Conclusions and Relevance

Although fulvestrant-palbociclib demonstrated significant antitumor activity, this randomized clinical trial failed to identify an improvement in progression-free survival with this regimen over letrozole-palbociclib in patients with endocrine-sensitive, hormone receptor-positive, ERBB2-negative advanced breast cancer.

Trial Registration

ClinicalTrials.gov Identifier: NCT02491983.

Long-Term Cardiac Safety and Survival Outcomes of Neoadjuvant Pegylated Liposomal Doxorubicin in Elderly Patients or Prone to Cardiotoxicity and Triple Negative Breast Cancer. Final Results of the Multicentre Phase II CAPRICE Study

Background

The CAPRICE trial was designed to specifically evaluate neoadjuvant pegylated liposomal doxorubicin (PLD) in elderly patients or in those with other cardiovascular risk factors in whom conventional doxorubicin was contraindicated. The primary analysis of the study showed a pathological complete response (pCR) of 32% and no significant decreases in LVEF during chemotherapy. Here, we report important secondary study objectives: 5-year cardiac safety, disease-free survival (DFS), overall survival (OS) and breast cancer specific survival (BCSS).

Methods

In this multicentre, single-arm, phase II trial, elderly patients or those prone to cardiotoxicity and high risk stage II-IIIB breast cancer received PLD (35 mg/m²) plus cyclophosphamide (600 mg/m²) every 4 weeks for 4 cycles, followed by paclitaxel for 12 weeks as neoadjuvant chemotherapy (NAC). Left ventricular ejection fraction (LVEF) monitorization, electrocardiograms and cardiac questionnaires were performed at baseline, during treatment and at 9, 16, 28 and 40 weeks thereafter. The primary endpoint was pCR and 5-year cardiac safety, DFS, BCSS and OS were also analyzed.

Results

Between Oct 2007, and Jun 2010, 50 eligible patients were included. Median age was 73 (35-84) years, 84% were older than 65; 64% of patients suffered from hypertension, and 10% had prior cardiac disease. Most of tumors (88%) were triple negative. No significant decreases in LVEF were observed. The mean baseline LVEF was 66.6% (52-86) and after a median follow-up of 5 years, mean LVEF was 66 (54.5-73). For intention to treat population, 5-year DFS was 50% (95% CI 40.2-68.1) and 5-year OS was 56% (95%CI 41.2-68.4). There were 8 non-cancer related deaths, achieving a 5 years BCSS of 67.74% (CI 95%:54.31%- 81.18%).

Conclusion

At 5-year follow-up, this PLD-based NAC regimen continued to be cardiac-safe and effective in a population of very high-risk breast cancer patients. This scheme should be considered as an option in elderly patients or in those with other risks of developing cardiotoxicity.

Trial Registration Number

ClinicalTrials.gov reference NCT00563953.

Oestrogen receptor activity in hormone-dependent breast cancer during chemotherapy

Background

Chemotherapy efficacy in early-stage hormone receptor-positive (HR+) breast cancer (BC) according to menopausal status needs a biological explanation.

Methods

We compared early-stage HR+ BC biological features before and after (neo)adjuvant chemotherapy or endocrine therapy (ET), and assessed oestrogen receptor (ER) pathway activity in both pre- and post-menopausal patients. The nCounter platform was used to detect gene expression levels.

Findings

In 106 post-menopausal patients with HR+/HER2-negative BC randomized to neoadjuvant chemotherapy or ET (letrozole+ribociclib), a total of 19 oestrogen-regulated genes, including progesterone receptor (PGR), were found downregulated in the ET-based arm-only. We confirmed this finding in an independent dataset of 20 letrozole-treated post-menopausal patients and found, conversely, an up-regulation of the same signature in HR+/HER2-negative MCF7 cell line treated with estradiol. PGR was found down-regulated by 2 weeks of ET+anti-HER2 therapy in pre-/post-menopausal patients with HR+/HER2-positive (HER2+) BC, while anti-HER2 therapy alone increased PGR expression in HR-negative/HER2+ BC. In 88 pre- and post-menopausal patients with newly diagnosed HR+/HER2-negative BC treated with chemotherapy, the 19 oestrogen-regulated genes were found significantly downregulated only in pre-menopausal patients. In progesterone receptor (PR)+/HER2-negative BC treated with neoadjuvant chemotherapy (n=40), tumours became PR-negative in 69.2% of pre-menopausal patients and 14.8% of post-menopausal patients (p=0.001). Finally, a mean decrease in PGR levels was only observed in pre-menopausal patients undergoing anti-HER2-based multi-agent chemotherapy.

Interpretation

Chemotherapy reduces the expression of ER-regulated genes in pre-menopausal women suffering from hormone-dependent BC by supressing ovarian function. Further studies should test the value of chemotherapy in this patient population when ovarian function is suppressed by other methods.

Funding

Instituto de Salud Carlos III, Breast Cancer Now, the Breast Cancer Research Foundation, the American Association for Cancer Research, Fundació La Marató TV3, the European Union's Horizon 2020 Research and Innovation Programme, Pas a Pas, Save the Mama, Fundación Científica Asociación Española Contra el Cáncer, PhD4MDgrant of “Departament de Salut”, exp SLT008/18/00122, Fundación SEOM and ESMO. Any views, opinions, findings, conclusions, or recommendations expressed in this material are those solely of the author(s).

Evaluation of pharmacodynamic (PD) and biologic activity in a preoperative window-of-opportunity (WOO) study of giredestrant (GDC-9545) in postmenopausal patients (pts) with estrogen receptor-positive, HER2-negative (ER+/HER2–) operable breast cancer (BC)

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Background: Modulation of ER activity and/or estrogen synthesis is the mainstay therapeutic strategy in ER+ BC treatment. Giredestrant is a highly potent, nonsteroidal oral selective ER degrader (SERD) that achieves robust ER occupancy and is effective regardless of ESR1 mutation status. The first short-term preoperative WOO study (NCT03916744) of giredestrant in ER+/HER2– operable BC was designed for dose selection, while providing an early readout of PD as measured by traditional immunohistochemistry (IHC) and transcriptional profiling by assessing treatment effects in paired tumor tissue pre/posttreatment. We present an interim analysis. Methods: Pts were assigned to 14 days’ preoperative treatment with 10, 30, or 100 mg PO giredestrant QD. Pts had newly diagnosed, stage I–III operable, ER+/HER2– untreated BC ≥1.5 cm in diameter (by ultrasound). Modulation of ER signaling and cell proliferation were assessed using paired formalin-fixed paraffin-embedded tumor specimens collected before and after ̃14 days of study treatment. ER, progesterone receptor (PR), and Ki67 protein levels were analyzed by IHC. Change from baseline in tumor cell proliferation by Ki67 was the primary endpoint. Gene expression analysis was performed using the Illumina TruSeq RNA Access method. Results: From Jul 26, 2019 to Oct 15, 2020, 46/75 biomarker-evaluable pts were enrolled across three dose cohorts (10 mg: n = 15; 30 mg: n = 18; 100 mg: n = 13). Pt demographics and tumor characteristics were similar across cohorts. Baseline PAM50 analysis classified tumors as Luminal A (77%) or B (23%). Giredestrant treatment resulted in robust and indistinguishable PD and biologic activity at all doses. Geometric mean posttreatment proportional reduction of Ki67 was 79% (95% CI: 69–89; 10 mg: 80%; 30 mg: 76%; 100 mg: 80%), and 51% of tumors exhibited complete cell cycle arrest, defined as Ki67 ≤2.7%. Mean posttreatment proportional reductions of ER and PR H-scores were 71% (95% CI: 67–75) and 60% (95% CI: 51–70), respectively. An analysis of a predefined, experimentally derived set of 38 ER target genes (the ‘ER activity signature’), was completed for 42 paired tumor specimens. Forty-one of 42 pts (98%) showed a posttreatment reduction in ER activity with a mean proportional decrease of 79% (95% CI: 70–88). A wide range of baseline ER activity was observed with no correlation to baseline ER or PR H-score, or Ki67. There were no discontinuations due to adverse events (AEs). A single grade 3 serious AE was reported in each cohort (all assessed as unrelated to giredestrant). No grade 4 or 5 AEs were reported. Conclusions: Giredestrant was well tolerated in the preoperative setting in ER+/HER2– operable BC, and PDs were consistent with the 30 mg dose achieving maximal ER inhibition. Clinical trial information: NCT03916744.

persevERA Breast Cancer (BC): Phase III study evaluating the efficacy and safety of giredestrant (GDC-9545) + palbociclib versus letrozole + palbociclib in patients (pts) with estrogen-receptor-positive, HER2-negative locally advanced or metastatic BC (ER+/HER2– LA/mBC)

TPS1103

Background: Modulating estrogen synthesis and/or ER activity is the mainstay of treatment for pts with ER+ BC. Despite substantial progress, many pts experience relapse during/after adjuvant endocrine therapy. However, even though resistant to aromatase inhibitors (AIs) or tamoxifen, growth and survival of the majority of tumors are thought to remain dependent on ER signaling. Therefore, pts with ER+ BC can still respond to second- or third-line endocrine treatment after progression on prior therapy (Di Leo 2010; Baselga 2012). Therapeutic resistance can arise from mutations in ESR1, which can drive estrogen-independent transcription and proliferation. The highly potent, non-steroidal oral selective ER degrader giredestrant achieves robust ER occupancy and is active regardless of ESR1 mutation status. Phase I data indicate that giredestrant is well tolerated, with encouraging activity as a single agent and in combination with the CDK4/6 inhibitor palbociclib (Lim 2020). Single-agent activity was observed after prior treatment with fulvestrant and/or a CDK4/6 inhibitor (Jhaveri 2019). Methods: persevERA BC (NCT04546009) is a double-blind, placebo-controlled, randomized, multicenter phase III study designed to evaluate the efficacy and safety of first-line giredestrant + palbociclib in pts with ER+/HER2– LA/mBC. Randomization: 1:1 to either giredestrant (30 mg PO) plus letrozole placebo QD or letrozole (2.5 mg PO) plus giredestrant placebo QD on Days 1–28 of each 28-day cycle, with palbociclib (125 mg PO QD) on Days 1–21 of each 28-day cycle. Men and premenopausal women will receive an LHRH agonist. Eligibility: females or males ≥18 years old with measurable disease or evaluable bone disease and no prior treatment for advanced disease. Pts who received prior fulvestrant or who have relapsed within 12 months of completion of (neo)adjuvant therapy with an AI and/or prior therapy with CDK4/6 inhibitor are not eligible; relapse during tamoxifen therapy but > 24 months after the start of tamoxifen therapy is allowed. Stratification: site of disease, disease-free interval since the end of (neo)adjuvant therapy, menopausal status, and geographic region. Primary efficacy endpoint: progression-free survival (determined locally by the investigator per RECIST v1.1). Secondary endpoints include overall survival, objective response rate, duration of response, clinical benefit rate, QoL, and safety. Enrollment is open (first patient in: Oct 9, 2020); target recruitment is 978 pts across all sites in a global enrollment phase. After completion of the global enrollment, additional pts may be enrolled in China. Clinical trial information: NCT04546009 .

Safety and activity of single-agent giredestrant (GDC-9545) from a phase Ia/b study in patients (pts) with estrogen receptor-positive (ER+), HER2-negative locally advanced/metastatic breast cancer (LA/mBC)

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Background: Targeting ER activity and/or E synthesis is a mainstay of ER+ BC treatment, but many pts relapse during/after adjuvant endocrine therapy (ET) or develop resistance via ESR1 mutations that drive E-independent transcription and proliferation. Most tumors remain ER signaling-dependent and pts may respond to second-/third-line ET after disease progression (PD) on prior therapies (Di Leo 2010; Baselga 2012). Giredestrant, a highly potent, nonsteroidal oral selective ER degrader, achieves robust ER occupancy, is active despite ESR1 mutations, and was well tolerated ± palbociclib with encouraging antitumor activity in the nonrandomized, open-label, dose-escalation and -expansion, phase Ia/b GO39932 study (NCT03332797; Jhaveri 2019; Lim 2020). We present updated interim data from the dose-escalation and -expansion single-agent giredestrant cohorts. Methods: Pts had ≤2 prior therapies in the LA/mBC setting with disease recurrence/PD while being treated with adjuvant ET for ≥24 mo and/or ET in the LA/mBC setting, and derived a clinical benefit (CB) from therapy (tumor response/stable disease [SD] ≥6 mo). Pts received 10, 30, 90/100, or 250 mg PO giredestrant QD on D1–28 of each 28-day cycle. Pts were postmenopausal (medical menopause on LHRH agonists was allowed with ≥100 mg giredestrant). Results: Clinical cutoff: Jul 31, 2020; median prior therapy lines in the LA/mBC setting: 1; mean dose intensity: 98%. Safety/activity: see the table below. No adverse events (AEs) led to study drug withdrawal. No dose-limiting toxicities (DLTs) occurred; maximum tolerated dose was not reached. Most common AEs in 107 pts: fatigue (22; 21%), arthralgia (18; 17%), and nausea (17; 16%); largely grade 1/2. Related grade 3 AEs were infrequent (5; 5%); none were grade 4/5 per investigator assessment (grade 5 duodenal perforation occurred with 90/100 mg after stopping giredestrant due to PD). 8 (7%) had bradycardia (none with 10 mg or the 30 mg phase 3 dose; all grade 1 except one grade 2 at 250 mg; no treatment interruptions/dose reductions were required). Objective responses and CB were observed at all doses. Conclusions: Single-agent giredestrant was well tolerated at all doses, with no DLTs. AEs were generally low grade and in keeping with expected AEs for ETs. Clinical activity was observed at all doses. Updated data, including biomarker and correlative data, will be presented. Clinical trial information: NCT03332797 .[Table: see text]

Abstract PS10-27: A phase II proof-of-concept study of palbociclib (P) rechallenge in patients (pts) with hormone receptor (HR)[+]/HER2[-] metastatic breast cancer (MBC) and clinical benefit to prior P-based treatment (BIOPER)

Background: The addition of a cyclin-dependent kinase 4-6 inhibitor (CDK4/6i) to letrozole or fulvestrant significantly improves progression-free survival (PFS) and overall survival (OS) in HR[+]/HER2[-] MBC pts. At present, the optimal endocrine treatment (ET) after progression on a CDK4/6i remains unknown. However, preliminary findings revealed drivers of adaptive resistance more frequently related to ET than to CDK4/6i. BIOPER explored the efficacy and safety of continuing the same CDK4/6i in combination with a different ET agent beyond progression on prior P-based regimen in HR[+]/HER2[-] MBC and assessed predictive biomarkers to identify those pts who are more likely to benefit from this strategy. Methods: BIOPER (NCT03184090) is a multicenter, non-controlled, phase II trial. Eligible pts included pre- and post-menopausal women aged ≥18 years with HR[+]/HER2[-] MBC that showed a confirmed progressive disease (PD) after having achieved clinical benefit (response or stable disease ≥24 weeks) on immediately prior P plus ET-based regimen. Up to two prior ET lines and not more than one line of prior chemotherapy for MBC were allowed. Pts received P (oral, 75/100/125 mg/day 3 weeks on/1 week off) combined with ET of physician’s choice (including tamoxifen, exemestane, fulvestrant, anastrozole, or letrozole) until PD or unacceptable toxicity. Co-primary endpoints were clinical benefit rate (CBR) -in terms of complete or partial response [PR] and stable disease lasting ≥24 weeks as per RECIST 1.1 (H0: CBR≤5% versus H1: CBR≥20%)- and tumor molecular alterations in the cyclin D-CDK 4/6-retinoblastoma pathway detected at baseline as markers of resistance and sensitivity to P rechallenge. Secondary endpoints included investigator-assessed PFS, objective response rate (ORR), OS, and safety using the Common Terminology Criteria for Adverse Events (AEs) 4.03. Results: Between June 15, 2017 and April 25, 2019, a total of 33 pts from 21 centers in 2 countries were enrolled. Among the 33 pts who were included in the safety set, 1 patient who did not achieve clinical benefit on prior P-based regimen was excluded from the efficacy analysis (n=32). The median age was 59.5 years (range 42-80 years) and all pts were post-menopausal. A total of 25 (78.1%) pts had visceral disease (56.3% of whom with liver metastases), 16 (50%) had ECOG 0, and 19 (59.4%) presented ≥3 metastatic sites. Of 32 pts, 15 (46.9%) received letrozole, 14 (43.8%) received fulvestrant, and 3 (9.4%) exemestane. The median PFS for the prior P-based regimen was 13.8 months (mo) (95% confidence interval [CI] 5.6-47.1 mo). The median number of prior ET and chemotherapy lines for MBC was 2 (range 1-4). By the data cutoff date, 26 PFS events occurred, 5 pts were still on treatment, and 1 patient discontinued treatment because of investigator’s decision. The CBR was 34.4% (95% CI 18.6-53.2%) reaching the prespecified primary endpoint. The ORR was 3.1% (95% CI 0.1-16.2%) with 1 patient with PR. The median PFS was 2.6 mo (95% CI 1.8-5.5 mo). With a median follow-up of 11.8 mo, the OS data were immature with a total of 8 deaths (25%). The incidence of all grade (G) and G 3 or 4 (G3-4) AEs were 90.9% and 48.5%, respectively. The most common G3-4 AEs were neutropenia (42.4%) and leukopenia (6.1%). No discontinuations due to AEs and treatment-related deaths occurred. A comprehensive molecular tumor profiling will be presented during the symposium. Conclusions: Prolonging CDK4/6 blockade beyond progression on prior P-based treatment achieved the prespecified clinical benefit among pts with HR[+]/HER2[-] MBC. This strategy is currently being evaluated in the randomized phase II PALMIRA trial. Further research is ongoing to identify patient subgroups who could benefit from this treatment strategy.

Citation Format: Antonio Llombart-Cussac, Javier Cortés, Beatriz Bellosillo Paricio, Miguel Gil Gil, Giuseppe Curigliano, José Manuel Pérez-García, Laura Comerma Blesa, Manuel Ruíz Borrego, Enrique Espinosa, Lourdes Calvo, Begoña Bermejo, Meritxell Bellet, Federico Rojo Todo, Juan de la Haba, Vanesa Quiroga, Alessandro Minisini, Ana Santaballa, Miguel Sampayo, Andrea Malfettone, Joan Albanell. A phase II proof-of-concept study of palbociclib (P) rechallenge in patients (pts) with hormone receptor (HR)[+]/HER2[-] metastatic breast cancer (MBC) and clinical benefit to prior P-based treatment (BIOPER) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-27.

Abstract PS10-17: Palbociclib (P) in combination with fulvestrant (F) or letrozole (L) in endocrine-sensitive patients (pts) with hormone receptor (HR)[+]/HER2[-] metastatic breast cancer (MBC): detailed safety analysis from a multicenter, randomized, open-label, phase II trial (PARSIFAL)

Background: P led to a meaningful improvement in clinical outcomes when used in combination with endocrine therapy for first- or later-line regimen in HR[+]/HER2[-] MBC. Grade 3-4 neutropenia was the most common adverse event (AE) in the P-containing regimens. Although venous thromboembolic events (VTE) have been rarely reported in registrational trials, a systematic review and meta-analysis of randomized controlled trials demonstrated a higher rate of these AEs. Moreover, rare but severe cases of interstitial lung disease (ILD)/pneumonitis have been observed during post-approval use of P. Here, we present a comprehensive toxicity profile of pts included in the PARSIFAL study, with particular emphasis given to AEs of special interest of the overall safety population. Methods: A total of 486 pts with HR[+]/HER2[-] MBC with no prior therapy in the advanced setting and endocrine sensitive criteria (relapse &gt;12 months [mo] after the end of adjuvant endocrine therapy or diagnosed with de novo metastatic disease) were randomly assigned 1:1 to receive P (oral 125 mg/day [d]; 3 weeks on/1 week off) plus either F (intramuscular injection 500 mg/d; d 0, 14, 28, and then every 28 ds) or L (oral 2.5 mg/d). Pts were stratified by visceral involvement and type of disease presentation (de novo/recurrent). Safety assessments included blood analysis and collection of vital signs at screening, d1 of each cycle, and end of treatment/withdrawal. Severity was graded as per the NCI Common Terminology Criteria for Adverse Events v.4.03. Results: The incidence rate of any grade, grade 3-4, and serious AEs was 99.6%, 80.9%, and 29.9%, respectively, in the FP arm, and 99.2%, 78.5%, and 21.1% in the LP arm. Discontinuations due to AEs were 5.4% in the FP arm and 2.1% in the LP arm. Neutropenia, leukopenia, anemia, asthenia, arthralgia, fatigue, and diarrhea were the most frequent AEs in both arms. Febrile neutropenia was reported in 1.2% (3 pts) and 0.4% (1 patient) in the FP and LP arms, respectively. The rate of VTE of any grade was 5.8% (14 pts) in the FP arm and 4.5% (11 pts) in the LP arm (p = 0.531). Among 18 pts who had grade ≥ 3 pulmonary embolism (PE), the incidence reported in the FP and LP arms was 5% (12 pts) vs 2.5% (6 pts), respectively, and many of them (n=16, 88.9%) were unrelated PE. Asymptomatic grade 3 PE was reported in 10 pts of the entire study population on every 3-mo CT scan. Further, in 5 pts PE was detected in the context of progressive disease. Median time from the first dose of study drugs to occurrence of PE was 4.1 mo (range 1.4-32.0 mo) in the FP arm and 7 mo (range 1.8-19.3 mo) in the LP arm. Analysis of baseline characteristics in the whole population revealed that older pts had a significantly increased risk for developing PE (69.5 years [range 47-84 years]; p &lt; 0.01). ECOG performance status, menopausal status, metastatic disease, visceral involvement, number of disease sites, and prior therapies including antithrombotic agents did not significantly increase the risk for developing PE. Grade 3 ILD/pneumonitis was rarely observed in the FP and LP arms (0.8% vs 1.2%, respectively) with no grade 4 AE. Conclusions: First-line treatment with FP and LP for HR[+]/HER2[-] MBC in the PARSIFAL study confirmed the favorable safety profile, with neutropenia representing the most common AE. Although rare, ILD/pneumonitis can be a side effect of P-based regimens. VTE and PE incidence rates were low and consistent with age-specific analyses from PALOMA trials and breast cancer population. Early detection of these AEs may assist in optimizing their management.

Citation Format: José Manuel Pérez-García, Antonio Llombart-Cussac, Meritxell Bellet, Florence Dalenc, Miguel J. Gil Gil, Manuel Ruiz Borrego, Joaquín Gavilá, Miguel Sampayo-Cordero, Elena Aguirre, Peter Schmid, Frederik Marmé, Serena Di Cosimo, Joseph Gligorov, Andreas Schneeweiss, Joan Albanell, Pilar Zamora, Duncan Wheatley, Eduardo Martínez-De Dueñas, Vicente Carañana, Kepa Amillano, Andrea Malfettone, Javier Cortés. Palbociclib (P) in combination with fulvestrant (F) or letrozole (L) in endocrine-sensitive patients (pts) with hormone receptor (HR)[+]/HER2[-] metastatic breast cancer (MBC): detailed safety analysis from a multicenter, randomized, open-label, phase II trial (PARSIFAL) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-17.

Abstract OT-26-02: Phase III open-label, multicenter, randomized trial of adjuvant palbociclib in combination with endocrine therapy versus endocrine therapy alone for patients with hormone receptor-positive / HER2-negative resected isolated locoregional recurrence of breast cancer - The POLAR Trial

Background: Isolated local or regional recurrence (ILRR) of breast cancer (BC) after mastectomy or lumpectomy indicates a poor prognosis and patients with ILRR hold a substantial risk of developing subsequent distant metastasis. Limited randomized evidence supports the recommendation of systemic treatment for hormone receptor-positive (HR+) lLRR. Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors, such as palbociclib, have shown activity and safety in the first-line treatment of metastatic HR+/HER2-negative BC.

The POLAR hypothesis is based on the results of the CALOR trial (IBCSG Trial 27-02), which showed effectiveness of adjuvant chemotherapy among patients with resected HR-negative ILRR, but not for HR+ ILRR. Considering these findings and compelling evidence supporting the activity of the combination of CDK4/6 inhibitors and endocrine therapy (ET), we hypothesize that palbociclib in combination with ET may be effective as adjuvant therapy in patients with HR+/HER2-negative resected ILRR of BC.

Trial design: POLAR is a phase III open-label, multicenter, randomized trial of adjuvant palbociclib in combination with standard ET versus standard ET alone for women and men with histologically confirmed HR+/HER2-negative resected ILRR of BC. Protocol treatment consists of palbociclib (125 mg/d orally for 21 days, followed by 7 days rest) for 3 years plus standard ET for at least 3 years (Arm A) or standard ET for at least 3 years (Arm B). Patients must be enrolled within 6 months of complete gross excision of the ILRR. Patients may have started standard ET prior to entry.

Randomization (1:1) is stratified according to (1) gender and menopausal status; (2) planned ET (oral aromatase inhibitor or tamoxifen vs. fulvestrant).

The primary endpoint, invasive disease-free survival (iDFS), will be compared between treatment groups using a stratified log-rank test. The sample size provides 80% power to detect a 50% reduction in hazard (HR=0.50) for palbociclib plus ET versus ET-alone, using a log-rank test with two-sided α=0.05 test with 66 iDFS events. The 3-year iDFS is assumed to be 76% on the basis of patients in the CALOR trial who had ER+ ILRRs.

Accrual: The trial will recruit 400 patients from approximately 50 Centers in Austria, France, Hungary, Italy, Spain and Switzerland. The first patient was randomized in August 2019. Accrual as of mid-June 2020 was 25 patients.

The POLAR trial (IBCSG 59-19 / BIG 18-02) is sponsored and coordinated by IBCSG with financial support from Pfizer. The trial is conducted under the BIG umbrella in collaboration with ABCSG, GEICAM, SOLTI, SAKK and Unicancer.

NCT03820830

Citation Format: Elisabetta Munzone, Stefan Aebi, Noelia Martínez Jañez, Uwe Güth, Meritxell Bellet, Barbara Pistilli, Marija Balic, Heidi Roschitzki-Voser, Meredith M Regan. Phase III open-label, multicenter, randomized trial of adjuvant palbociclib in combination with endocrine therapy versus endocrine therapy alone for patients with hormone receptor-positive / HER2-negative resected isolated locoregional recurrence of breast cancer - The POLAR Trial [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-26-02.

The proapoptotic gene interferon regulatory factor-1 mediates the antiproliferative outcome of paired box 2 gene and tamoxifen

Tamoxifen is the most prescribed selective estrogen receptor (ER) modulator in patients with ER-positive breast cancers. Tamoxifen requires the transcription factor paired box 2 protein (PAX2) to repress the transcription of ERBB2/HER2. Now, we identified that PAX2 inhibits cell growth of ER+/HER2- tumor cells in a dose-dependent manner. Moreover, we have identified that cell growth inhibition can be achieved by expressing moderate levels of PAX2 in combination with tamoxifen treatment. Global run-on sequencing of cells overexpressing PAX2, when coupled with PAX2 ChIP-seq, identified common targets regulated by both PAX2 and tamoxifen. The data revealed that PAX2 can inhibit estrogen-induced gene transcription and this effect is enhanced by tamoxifen, suggesting that they converge on repression of the same targets. Moreover, PAX2 and tamoxifen have an additive effect and both induce coding genes and enhancer RNAs (eRNAs). PAX2-tamoxifen upregulated genes are also enriched with PAX2 eRNAs. The enrichment of eRNAs is associated with the highest expression of genes that positivity regulate apoptotic processes. In luminal tumors, the expression of a subset of these proapoptotic genes predicts good outcome and their expression are significantly reduced in tumors of patients with relapse to tamoxifen treatment. Mechanistically, PAX2 and tamoxifen coexert an antitumoral effect by maintaining high levels of transcription of tumor suppressors that promote cell death. The apoptotic effect is mediated in large part by the gene interferon regulatory factor 1. Altogether, we conclude that PAX2 contributes to better clinical outcome in tamoxifen treated ER-positive breast cancer patients by repressing estrogen signaling and inducing cell death related pathways.

Personalized cancer therapy prioritization based on driver alteration co-occurrence patterns

Identification of actionable genomic vulnerabilities is key to precision oncology. Utilizing a large-scale drug screening in patient-derived xenografts, we uncover driver gene alteration connections, derive driver co-occurrence (DCO) networks, and relate these to drug sensitivity. Our collection of 53 drug-response predictors attains an average balanced accuracy of 58% in a cross-validation setting, rising to 66% for a subset of high-confidence predictions. We experimentally validated 12 out of 14 predictions in mice and adapted our strategy to obtain drug-response models from patients’ progression-free survival data. Our strategy reveals links between oncogenic alterations, increasing the clinical impact of genomic profiling.

PARSIFAL: A randomized, multicenter, open-label, phase II trial to evaluate palbociclib in combination with fulvestrant or letrozole in endocrine-sensitive patients with estrogen receptor (ER)[+]/HER2[-] metastatic breast cancer

1007

Background: The CDK4/6 inhibitor palbociclib (P) in combination with letrozole (L) has become a standard first-line treatment for patients (pts) with luminal metastatic breast cancer (MBC) (PALOMA-1 & 2 trials). Meanwhile, the anti-estrogen fulvestrant (F) showed to be superior to anastrozole in the same population (FALCON trial). We aimed to identify the best endocrine agent to combine with P in this first-line scenario. Methods: A total of 486 pts with ER[+]/HER2[-] MBC with no prior therapy in the advanced setting and endocrine sensitive criteria (relapse > 12 months [mo] after the end of adjuvant endocrine therapy or diagnosed with “de novo” metastatic disease) were randomly assigned (1:1 ratio) to receive P (oral 125 mg/day [d]; 3 wks on/1 wk off) plus F 500 mg/d (I.M Days 0, 14, 28, and then every 28 d) or PL (oral 2.5 mg/d). Pts were stratified by visceral involvement and type of disease presentation (“de novo”/recurrent). Primary endpoint was investigator-assessed progression-free survival (PFS). Secondary endpoints included overall survival (OS), overall response rate (ORR), clinical benefit rate (CBR), and safety. 254 events were needed with 80% power to detect a hazard ratio (HR) ≤0.7 in favor of PF (2-sided α = 0.05). Results: By March 9th, 2020, 256 PFS events occurred. Pts characteristics were well balanced. Median age was 62 years (range: 25–90), 56.6% were ECOG 0, 40.7% had “de novo” metastatic disease, 48% had visceral disease, and 43.6% with ≥3 organ sites involved. At median follow-up of 32 mo, median PFS was 27.9 mo (95% confidence interval [CI], 24.2-33.1) with PF and 32.8 mo (95% CI, 25.8-35.9) with PL (HR: 1.1; 95% CI, 0.9-1.5; P = 0.321). No differences were observed for pts with or without visceral involvement (HR: 1.3 and HR: 0.97 respectively, interaction P = 0.275), and for “de novo” or recurrent metastatic disease (HR: 1.1 and HR: 1.1 respectively, P = 0.979). The 4-year OS rate was 67.6% in PF and 67.5% in PL arm (HR: 1; 95% CI, 0.7-1.5; P = 0.986). No differences were observed in ORR or CBR between arms. Grade ≥3 adverse events were similar in both arms, being neutropenia and leukopenia the most frequent. No treatment-related deaths were reported. Conclusion: This study was not able to identify an improvement in PFS for PF over PL in patients with endocrine-sensitive ER[+]/HER2[-] MBC. As both arms demonstrated comparable 4 years-OS, PF is a reasonable alternative to PL in this setting. Clinical trial information: NCT02491983 .

A phase Ib study to evaluate the oral selective estrogen receptor degrader GDC-9545 alone or combined with palbociclib in metastatic ER-positive HER2-negative breast cancer

1023

Background: GDC-9545 is a potent, orally available, selective estrogen receptor degrader developed for the treatment of ER-positive (ER+) breast cancer alone or combined with CDK4/6 inhibitors. A first-in-human study evaluated 10-250 mg GDC-9545; tolerability, pharmacokinetic (PK), pharmacodynamic (PD), and clinical results support expansion cohorts at ≥30 mg (Jhaveri et al., 2019). Methods: This study evaluated PK, PD, and efficacy of GDC-9545 alone and combined with palbociclib, ± LHRH agonist. Eligible patients (pts) had ER+ (HER2-) metastatic breast cancer (MBC) with ≤ 2 prior therapies in the advanced or metastatic setting. No prior treatment with CDK4/6 inhibitor was allowed in pts receiving palbociclib. Results: Eight-five pts were enrolled in 2 cohorts: GDC-9545 100 mg given once daily ± LHRH agonist (Cohort A), and GDC-9545 100 mg +125 mg palbociclib on a 21 day on/7 day off schedule ± LHRH agonist (Cohort B). Of the 39 pts in Cohort A, adverse events (AE) occurring in ≥10% of pts were fatigue, cough, back pain, pain in extremity, and arthralgia. Related AEs were generally Grade (G) 1-2; there were 3 related G3 AEs of fatigue, transaminase increased, and diarrhea. Two pts had GDC-9545 reduced, one due to G3 diarrhea and another due to G3 transaminitis. Of the 46 pts in Cohort B, AEs in ≥10% of pts were neutropenia, fatigue, bradycardia, diarrhea, constipation, dizziness, nausea, anemia, asthenia, thrombocytopenia, pruritus, and visual impairment. Twenty-six (57%) pts had G≥3 AEs. G≥3 neutropenia was reported in 23 (50%) pts. One pt had palbociclib reduced due to G3 febrile neutropenia. Eleven (13%) of 85 pts had G1 asymptomatic bradycardia considered related to GDC-9545. No pts in either cohort discontinued study treatment due to AEs. PK analysis and clinical data demonstrate no clinically relevant drug-drug interactions between GDC-9545 and palbociclib. Reduced ER, PR, and Ki67 levels, and an ER activity signature, were observed in paired pre- and on-treatment biopsies (n = 12). Eighteen of 33 pts in Cohort A had either confirmed partial responses or were on study 24 weeks (clinical benefit rate 55%). Clinical benefit was observed in pts with prior fulvestrant treatment and with detectable ESR1 mutations at enrollment. Clinical benefit data for both cohorts are anticipated to be mature in April 2020. Conclusions: GDC-9545 was well-tolerated as a single agent and in combination with palbociclib with encouraging PK, PD, and anti-tumor activity in ER+ MBC to support Phase III development. Clinical trial information: NCT03332797 .

Abstract P4-10-17: Baseline and pharmacodynamic changes of circulating exosomal microRNAs predict early versus late progression to palbociclib plus endocrine therapy in patients with metastatic breast cancer. A sub-analysis of the PARSIFAL-1 trial

BACKGROUND: Palbociclib in combination with endocrine therapy (ET) is the first- or second-line standard of care for patients (pts) with hormone receptor (HR)-positive (+)/human epidermal growth factor receptor 2 (HER2)-negative (-) metastatic breast cancer (MBC). No clinically validated markers of long-term benefit from palbociclib have been established and the clinically relevant resistance mechanisms to cyclin-dependent kinases 4 and 6 inhibitors remain undefined. In the present study, we explored candidate circulating exosomal microRNAs (miRNAs) as putative predictors of benefit and/or resistance to palbociclib in combination with ET in pts included in the PARSIFAL-1 trial (ClinicalTrials.gov identifier: NCT02491983). MATERIALS AND METHODS: PARSIFAL-1 was a randomized, open-label, phase II trial aimed at evaluating the efficacy and safety of palbociclib plus either fulvestrant or letrozole in HR+/HER2- MBC pts. For the study of exosomal miRNAs, forty-five consenting pts were selected based on primary endocrine resistance according to the ABC-4 criteria. Nine pts who progressed within the first six months after treatment initiation in the absence of an objective response were considered Resistant and thirty-six pts who progressed more than six months after starting therapy were classified as Sensitive. Exosomes were isolated from plasma samples collected at study entry (baseline) and after 12 weeks of treatment initiation. Differences in miRNA expression between Resistant and Sensitive pts as well as miRNA pharmacodynamic changes between baseline and 12-week samples were assessed. Ribonucleic acid (RNA) was isolated using the miRNeasy plasma kit and the library preparation was done using the QIAseq miRNA library kit according to manufacturer’s instructions. All experiments were conducted at QIAGEN Genomic Services in Germany. Differential expression of miRNA between different conditions was studied using EdgeR statistical software package from Bioconductor. Estimated p-values for significantly differentially expressed miRNAs were adjusted using Benjamini-Hochberg’s False Discovery Rate (FDR). Differences in expression of miRNA with an FDR below 0.05 were considered significant. RESULTS: Sequencing of exosomal RNA and preparation of miRNA libraries were successful for all included samples, with good technical performance. On average, 2.8 million Unique Molecular Index-corrected reads were obtained for each sample and the average percentage of mappable reads was 34.5%. Overall, expression of miRNAs was higher in Resistant compared with Sensitive pts. Eight miRNAs were called as differentially expressed between the two groups. Four miRNAs (miR-1246; miR-375; miR-193a-5p; miR-181d-5p) were differentially expressed at baseline, three (miR-196a-5p, miR-200a-3p, miR-320d) were differentially expressed at 12 weeks, and expression of one miRNA (miR-141-3p) was consistently higher across both time points in Resistant pts. Significant pharmacodynamic changes in miRNA expression were observed both in Resistant and Sensitive pts. Seven miRNAs (miR-224-5p, miR-16-5p, let-7a-5p, miR-381-3p, miR-200c-3p, miR-493-3p, let-7b-5p) in Sensitive pts and three miRNAs (miR-223-3p, miR-126-3p, miR-320b) in Resistant pts were differentially expressed between baseline and 12-week samples. CONCLUSIONS: Circulating exosomal miRNA profiling is feasible in liquid biopsies from MBC pts. Differential expression of selected miRNAs at baseline or their pharmacodynamic modulation may predict benefit from palbociclib combined with ET in pts with HR+/HER2- MBC. Validation of the most promising miRNAs by custom quantitative PCR is warranted.

Citation Format: David Casadevall, Joan Albanell Mestres, Federico Rojo, Beatríz Bellosillo, Abel González, Violeta Serra, Meritxell Bellet, Miguel Angel Gil, Miquel Angel Pujana, Angelo Gámez, Enrique Espinosa, Peter Schmid, Joseph Gligorov, Frederik Marmé, Carlos L. Arteaga, Leonardo Mina, Andrea Malfettone, Miguel Sampayo, José Manuel Pérez-García, Javier Cortés, Antonio Llombart-Cussac. Baseline and pharmacodynamic changes of circulating exosomal microRNAs predict early versus late progression to palbociclib plus endocrine therapy in patients with metastatic breast cancer. A sub-analysis of the PARSIFAL-1 trial [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-10-17.

34Efficacy and safety of various doses of the new dual endothelin receptor antagonist aprocitentan in the treatment of hypertension

Background

Endothelin Receptor Antagonists (ERAs) have been investigated for the treatment of a variety of cardiovascular conditions because of their potent vasodilating properties. However, until now, ERAs have only been registered for the treatment of pulmonary arterial hypertension and scleroderma-induced digital ulcers. This class of drugs may also be useful in the treatment of difficult to control hypertension with a medical need.

Purpose

To investigate the efficacy and safety of various doses of the new dual ERA, aprocitentan, in the treatment of hypertension in order to determine the most appropriate dose(s) for further clinical development using an unattended, automated office BP (AOBP) device (BpTRU). This Phase 2 trial was registered at ClinicalTrials.gov [NCT02603809].

Methods

Eligible patients with hypertension (mean sitting systolic/diastolic BP 149.7/97.6 mmHg) received aprocitentan 5, 10, 25 or 50 mg, matching placebo or lisinopril 20 mg as a positive control, once daily for 8 weeks using a randomised, double-blind, parallel-group study design. AOBP was assessed at baseline and weeks 2, 4, 8, and 10 (withdrawal) by recording multiple BP readings with the patient resting quietly. Additionally, 24 h ambulatory BP monitoring was performed at baseline and week 8.

Results

A total of 490 eligible patients were randomised to the double-blind phase with 430 subjects successfully completing 8 weeks of treatment. Decreases in sitting systolic/diastolic AOBP, from baseline to week 8 were 10.3/6.3, 15.0/9.9, 18.5/12.0 and 15.1/10.0 mmHg for aprocitentan 5, 10, 25, and 50 mg, respectively vs. 7.7/4.9 mmHg for placebo and 12.8/8.4 mmHg for lisinopril. No changes in heart rate or body weight were observed for any dose of aprocitentan.

Modelling the dose-response suggested that the maximal effect of aprocitentan is achieved at a dose of approximately 25 mg and that 70% of this effect is already observed at a dose of 10 mg. Aprocitentan treatment was associated with decreases in haemoglobin, haematocrit, and albumin which exhibited a monotonic dose-response relationship, in line with its known vasodilating effects. Estimated increases in plasma volume were 3.0%, 5.1%, 6.9%, and 9.5% for aprocitentan 5, 10, 25, and 50 mg, respectively, vs. 1.6% for lisinopril and a decrease of 0.3% for placebo. All these values are below the accepted pathophysiological threshold of 10%.

The overall incidence of adverse events observed in the aprocitentan groups (ranging from 22.0% to 40.2%) was similar to that seen in the placebo group (36.6%). Overall, the most common events were hypertension, headache, and nasopharyngitis.

Conclusions

These findings support the use of aprocitentan at doses between 10 and 25 mg for further investigation as a potential treatment for hypertension.

Acknowledgement/Funding

Actelion conducted study. Drug discovery & early clinical pipeline demerged during Johnson & Johnson acquisition. Idorsia supported abstract.

Oral metronomic vinorelbine combined with endocrine therapy in hormone receptor-positive HER2-negative breast cancer: SOLTI-1501 VENTANA window of opportunity trial

Background

The biological effect of oral metronomic vinorelbine (mVNB) alone or in combination with endocrine therapy in patients with hormone receptor-positive (HR+)/HER2-negative breast cancer has been scarcely addressed.

Methods

Postmenopausal women with untreated stage I–III HR+/HER2-negative breast cancer were randomized (1:1:1) to receive 3 weeks of letrozole (LTZ) 2.5 mg/day, oral mVNB 50 mg 3 days/week, or the combination. The primary objective was to evaluate, within PAM50 Luminal A/B disease, if the anti-proliferative effect of LTZ+mVNB was superior to monotherapy. An anti-proliferative effect was defined as the mean relative decrease of the PAM50 11-gene proliferation score in combination arm vs. both monotherapy arms. Secondary objectives included the evaluation of a comprehensive panel of breast cancer-related genes and safety. An unplanned analysis of stromal tumor-infiltrating lymphocytes (sTILs) was also performed. PAM50 analyses were performed using the nCounter®-based Breast Cancer 360™ gene panel, which includes 752 genes and 32 signatures.

Results

Sixty-one patients were randomized, and 54 paired samples (89%) were analyzed. The main patient characteristics were mean age of 67, mean tumor size of 1.7 cm, mean Ki67 of 14.3%, stage I (55.7%), and grades 1–2 (90%). Most baseline samples were PAM50 Luminal A (74.1%) or B (22.2%). The anti-proliferative effect of 3 weeks of LTZ+mVNB (− 73.2%) was superior to both monotherapy arms combined (− 49.9%; p = 0.001) and mVNB (− 19.1%; p < 0.001). The anti-proliferative effect of LTZ+mVNB (− 73.2%) was numerically higher compared to LTZ (− 65.7%) but did not reach statistical significance (p = 0.328). LTZ+mVNB induced high expression of immune-related genes and gene signatures, including CD8 T cell signature and PDL1 gene and low expression of ER-regulated genes (e.g., progesterone receptor) and cell cycle-related and DNA repair genes. In tumors with ≤ 10% sTILs at baseline, a statistically significant increase in sTILs was observed following LTZ (paired analysis p = 0.049) and LTZ+mVNB (p = 0.012). Grade 3 adverse events occurred in 3.4% of the cases.

Conclusions

Short-term mVNB is well-tolerated and presents anti-proliferative activity alone and in combination with LTZ. The high expression of immune-related biological processes and sTILs observed with the combination opens the possibility of studying this combination with immunotherapy. Further investigation comparing these biological results with other metronomic schedules or drug combinations is warranted.

Trial registration

NCT02802748, registered 16 June 2016.

Supplementary information

Supplementary information accompanies this paper at 10.1186/s13058-019-1195-z.

Changes in dietary intake, plasma carotenoids and erythrocyte membrane fatty acids in breast cancer survivors after a lifestyle intervention: results from a single-arm trial

BACKGROUND

The influence of nutrition on breast cancer prognosis is still inconclusive and therefore dietary interventions incorporating dietary biomarkers are needed to confirm compliance with dietary goals and clarify biological mechanisms. The present study assessed whether a lifestyle intervention in breast cancer survivors could affect dietary biomarkers of fruit and vegetables and fatty acids.

METHODS

In this phase II single-arm trial, 37 overweight/obese early stage breast cancer patients completed a 12-week diet and exercise intervention. The intervention involved 1-h weekly diet sessions delivered by a dietician and 75-min bi-weekly physical activity sessions of moderate-to-high intensity led by trained monitors. Before and after the intervention, three 24-h dietary recalls were carried out to calculate nutrient intakes and, in addition, blood samples were taken to measure plasma carotenoids, vitamin E and retinol concentrations and erythrocyte membrane fatty acid (EFA) composition. Wilcoxon signed rank tests were used to assess changes in dietary and biomarkers measurements over the intervention period.

RESULTS

After the intervention, there was a significant increase in the intake of dietary carotenoids (+15.1% compared to baseline) but not plasma carotenoids levels (+6.3%). Regarding the EFA levels, we observed a significant decrease in percentage of saturated fatty acids (-1.4%) and n-6 polyunsaturated fatty acids (-2.9%) and an increase in monounsaturated fatty acids (1.7%) and total and long-chain n-3 polyunsaturated fatty acids (by 13.1% and 13.7%, respectively). A favourable decrease in the ratio of long-chain n-6 to n-3 polyunsaturated fatty acids (-9.1%) was also observed.

CONCLUSIONS

After a short-term diet and exercise intervention in overweight/obese breast cancer survivors, we observed significant changes in dietary nutrients and fatty acid biomarkers, suggesting positive dietary changes that could be relevant for breast cancer prognosis.

Abstract CT219: Neoadjuvant letrozole and palbociclib in stage II-IIIB HR[+]/HER2[-] breast cancer with Oncotype DX Recurrence Score® (RS) 18-25 or 26-100. Analysis of RS changes at surgery (DxCARTES trial)

BACKGROUND: The combination of a CDK4/6 inhibitor (palbociclib, abemaciclib, or ribociclib) with an aromatase inhibitor (AI) significantly reduces Ki67 compared to single-agent AI in the neoadjuvant setting, but the rates of pathological complete response (pCR) or residual cancer burden (RCB) 0-I remain modest. Despite this inadequate pathological downstaging, to date, there is no data about the efficacy of this treatment in terms of molecular downstaging detected by a more refined genomic signature than Ki67, such as the Oncotype DX Breast Recurrence Score® (RS) test. The aim of this trial is to validate the ability of neoadjuvant palbociclib plus letrozole to modify two initial intermediate or high RS tumor cohorts.

TRIAL DESIGN: This is an international, multicenter, open-label, non-comparative, phase II trial. Main selection criteria include: (1) Pre- or post-menopausal women with treatment-naïve, centrally assessed, HR-positive/HER2-negative, Ki67 ≥ 20%, and stage II-IIIB breast cancer; (2) Pre-treatment RS result ≥ 18; (3) Patients agree to collect tissue samples at screening, at Cycle 1 Day 14 of treatment, and at surgery. Patients will be allocated, according to the pre-treatment RS result, either to Cohort A (RS 18-25) or Cohort B (RS 26-100) and will receive treatment with palbociclib (125 mg QD, 3/1 schedule) in combination with letrozole (2.5 mg QD, every 28-day cycle), ± LHRH analogs if pre-menopausal status, for 24 weeks. Definitive breast surgery will be performed within 7 days after completion of 6 treatment cycles. The primary objective of the study is to explore the ability of palbociclib in combination with letrozole to induce global molecular changes, measured by either the post-treatment RS result at surgery, or pCR. Secondary objectives include: (1) Concordance rate among post-treatment RS result and RCB, Ki67, and preoperative endocrine prognostic index (PEPI) score; (2) Overall response rate; (3) Safety-related outcome as per Common Terminology Criteria for Adverse Events v. 5.0. Patients will be accrued in a Simon’s two-stage design trial: optimal design in Cohort A and minimax design in Cohort B. With a unilateral type one error (alpha) set at 0.025 and a 0.8 power (type two error beta = 0.2), the required number of evaluable patients are 28. Considering a drop-out rate no lower than 10%, a sample size of 33 patients in each cohort will be needed. First Patient First Visit: Expected on April 2019.

Citation Format: Antonio Llombart Cussac, José Pérez-García, Ángel Guerrero, Begoña Bermejo, Miguel Gil, Vicente Carañana, Serafín Morales, Juan de la Haba, María Fernández, Emilio Alba, Ander Urruticoechea, Lourdes Calvo, Mireia Margeli, Antonio Antón, Manuel Ruíz Borrego, Joan Albanell, Pedro Sánchez Rovira, Meritxell Bellet, Sofia Braga, Passos Coelho, Miguel Abreu, Javier Cortés. Neoadjuvant letrozole and palbociclib in stage II-IIIB HR[+]/HER2[-] breast cancer with Oncotype DX Recurrence Score® (RS) 18-25 or 26-100. Analysis of RS changes at surgery (DxCARTES trial) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT219.

Determinants of concordance in clinically relevant genes (CRG) from synchronously acquired tumor biopsies (tBx) and ctDNA in metastatic breast cancer (MBC)

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Background: NGS in ctDNA from MBC is feasible and results may be informative for patients’ management, especially in non-luminal tumors (Oliveira et al, ASCO 2018). We aimed to study the determinants of concordance in CRG in a cohort of 60 MBC patients undergoing tBx and ctDNA collection. Methods: MiSeq Amplicon-based NGS (59 cancer-related genes) was performed in one single metastatic lesion per patient and compared with liquid biopsies taken at the same time point at disease progression to prior treatment. The concordance in CRG ( PIK3CA, AKT1, ERBB2, ESR1, PTEN, BRAF, FGFR1, HRAS, KRAS, and PIK3R1) in tBx vs ctDNA was determined at patient and at mutation (mut) level and correlated with mutant allele fraction (MAF), total disease volume (TDV), and clinical characteristics. True positive in plasma (TPP): patient with a mut detected both in ctDNA and tBx. TDV was defined as all metastasis volume assessed by CT scan (excluding sclerotic bone metastasis), and analyzed by an experienced radiologist using the 3DSlicer semiautomatic segmentation tool (TDV = pixel size x number of pixels). Results: Concordance in CRG at patient and mut level was 72% and 55%, respectively. Concordance for ERBB2 (1/1; 100%) and PIK3CA (17/22; 77%) was higher than for ESR1 (8/20; 40%) and AKT1 (2/6; 33%). ctDNA failed to detect 14 mut present in tBx ( ESR1 n = 5, PIK3CA n = 5, AKT1 n = 3, BRAF n = 1). Concordance was 100% for non-luminal and 60% for luminal cases (P = 0.01). In univariate analysis, concordance was not associated with MAF in tBx (P = 0.15), TDV (p = 0.86), number of prior lines of therapy (P = 0.57), number of metastatic sites (P = 0.56) or presence of visceral metastasis (P = 1.0). In patients with PIK3CA mut (N = 22), those with TPP had a numerically higher TDV than those where a PIK3CA mut was not detected in ctDNA (20.9cm3 vs 5.1cm3, P = 0.28). Across all patients, in the multivariate logistic model adjusted for other factors, TDV was a determinant of TPP (OR 1.02, 95%CI 1.0-1.06; P = 0.059). For each increase of 1cm3 in TDV, there was a 2% increase in the probability of detecting a mut in ctDNA. Conclusions: Our results suggest that liquid biopsy testing for the detection of actionable CRG is clinically valid in MBC, although its yield depends on several factors – tumor subtype, analyzed gene, and possibly tumor volume – that reflect both tumor heterogeneity and tumor shedding rate. Due to the potential clinical implications, the observation that mutation detection in ctDNA may correlate with tumor volume merits further study in a larger dataset.

Palbociclib and ribociclib in breast cancer: consensus workshop on the management of concomitant medication

Drug–drug interactions are of significant concern in clinical practice in oncology, particularly in patients receiving Cyclin-dependent kinase (CDK) 4/6 inhibitors, which are typically exposed to long-term regimens. This article presents the highlights from the ‘First Workshop on Pharmacology and Management of CDK4/6 Inhibitors: Consensus about Concomitant Medications’. The article is structured into two modules. The educational module includes background information regarding drug metabolism, corrected QT (QTc) interval abnormalities, management of psychotropic drugs and a comprehensive review of selected adverse effects of palbociclib and ribociclib. The collaborative module presents the conclusions of the five working groups, each of which comprised five experts from different fields. From these conclusions positive lists of drugs for treating common comorbid conditions that can be safely administered concomitantly with palbociclib and/or ribociclib were developed.

Abstract P6-18-17: Ribociclib + letrozole in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) advanced breast cancer (aBC) with no prior endocrine therapy (ET) for ABC: CompLEEment-1 trial, preliminary results from Spanish population

Background: The phase III Monaleesa-2, Monaleesa-3 and Monaleesa-7 trials have shown significantly improved PFS for the combination ribociclib + ET vs ET + placebo in pre-, peri-, and postmenopausal women with HR+/HER2–, first and second line aBC. The Compleement-1 trial is a phase IIIb, single-arm, open-label, international study to assess the safety and efficacy of ribociclib + letrozole in men and women who have not received prior ET for HR+, HER2– ABC [J Clin Oncol 36, 2018 (suppl; abstr 1056)].

Methods: 526 patients with HR+, HER2– ABC, ≤1 line of prior CT, and no prior ET for aBC were enrolled in the Compleement-1trial in Spain from April 2017 to January 2018. Patients received ribociclib (600 mg/day, 3 weeks on/1 week off) + letrozole (2.5 mg/day); men and premenopausal women received concomitant goserelin (3.6 mg subcutaneous implant every 28 days). The primary objective was safety and tolerability. Here we report on a sub-analysis from the Spanish population of Compleement-1 trial including baseline characteristics and early safety results for the first patients enrolled who completed at least 56 days of follow-up or discontinued before the cut-off date (3rd Oct 2017).

Results: One hundred fifty four patients constituted the analytical cohort for this sub-analysis. Demographics and baseline characteristics: median age was 52 years (range 24-82); 1% of patients were male, 31.8% female pre-menopausal and 67.5% female post-menopausal; 44.2% vs 38.3% of patients had visceral disease vs bone only disease; 49.9% patients had ≥2 metastatic sites; and 34.4% of patients presented as de novo stage IV. The median exposure for study treatment was 1.8 months (range 0.8-1.8). The grade 3/4 events reported &gt;1% included neutropenia (50%), increased GGT levels (3.2%), leukopenia (1.3%), and increased ALT (1.3%). QTcF prolongation &gt;480ms based on ECG data was reported in 1.2% patients. Median dose intensity for ribociclib was 600mg/day (range 476.5-600); 11% of patients required one dose reduction (8.4% due to AEs), 59.7% had at least one dose interruption (57.1% due to AEs) and 9.7% were permanently discontinued (4.5% due to AEs).

Conclusions: Preliminary safety results from this Compleement-1 sub-analysis including Spanish population are consistent with previous data presented from Monaleesa-2, Monaleesa-3, Monaleesa-7 and Compleement-1. These data support the predictable and manageable safety profile of ribociclib in combination with letrozole. Clinical trial information: NCT02941926

Citation Format: Salvador J, Ciruelos EM, Prat A, Jiménez-Rodríguez B, de la Cruz L, Martínez N, Villanueva Vázquez R, de Toro R, Antón A, Moreno F, Alvarez I, Gavila J, Quiroga V, Vicente E, de la Haba J, González-Santiago S, Díaz N, Barnadas A, Cantos Sánchez de Ibargüen B, Delgado JI, Bellet M, Gimeno A, Sanz S, Martin M. Ribociclib + letrozole in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) advanced breast cancer (aBC) with no prior endocrine therapy (ET) for ABC: CompLEEment-1 trial, preliminary results from Spanish population [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-18-17.

Abstract P5-11-01: Phamacodynamic and circulating tumor DNA evaluation in a phase I study of GDC-0927, a selective estrogen receptor antagonist/ degrader (SERD)

Background: Modulation of estrogen activity and/or synthesis is the mainstay therapeutic strategy in the treatment of ER positive breast cancer. However, despite the effectiveness of available endocrine therapies, many patients ultimately relapse or develop resistance to these agents via estrogen-dependent and estrogen-independent mechanisms, including mutations in ESR1 affecting the ER ligand binding domain that drive ER-dependent transcription and proliferation in the absence of estrogen. Based on preclinical and clinical data, SERDs are expected be effective in patients harboring ESR1 mutations. Biomarker analysis was performed on plasma and tumor samples from the Phase I study of GDC-0927 in metastatic breast cancer (Dickler et al, SABCS 2017) with the goal of evaluating activity in both ESR1 mutant and wildtype tumors, and to assess ER pathway modulation.

Methods: Hotspot mutations in ESR1, PIK3CA, and AKT1 were analyzed in baseline, on-treatment and end of treatment plasma derived circulating tumor DNA (ctDNA) using the BEAMing assay in patients treated at multiple dose levels of GDC-0927. A subset of samples was analyzed with Foundation Medicine's next generation sequencing ctDNA assay (FACT), which covers genomic alterations in 62 commonly altered genes. Paired pre- and on-treatment biopsies were collected to assess ER pathway modulation. ER, PR, and Ki67 protein levels were analyzed by immunohistochemistry. Gene expression analysis was performed using Illumina's RNA Access library preparation kit followed by paired-end (2x50b, 50M reads) sequencing on the HiSeq.

Results: Baseline and on-treatment plasma samples were available for 40 patients. ESR1 and PIK3CA mutations were observed in 52% and 33% of patient baseline samples, respectively (BEAMing method). Mutant allele frequencies (MAF) generally declined in the first on-treatment samples collected for both ESR1 (16 out of 21 samples) and PIK3CA (7 out of 12 samples). The majority of the reductions were greater than 95% relative to baseline. Increases in ESR1 MAFs were observed in later time-points and were not associated with any particular ESR1 mutation. There were six instances for which an ESR1 mutation was detected in an on-treatment sample that was not detected in the baseline sample, three at L536P and one each at D538G, L536H, and S463P, and four out of six with MAFs close to the limit of detection. The FACT assay also detected alterations in CDH1, NF1, PTEN, and TP53 in baseline samples. The relationship between MAF changes and clinical benefit to GDC-0927 will be presented. A predefined, experimentally-derived set of ER target genes were evaluated in pre- and on-treatment tumor biopsy pairs from six patients. Four of the six patients showed evidence of suppression in ER pathway activity, one patient treated at the 1000 mg dose level and three at the 1400 mg dose. The degree of pathway suppression was associated with pre-treatment pathway levels and decreases of ER and Ki67 protein levels.

Conclusions: We report here evidence of consistent reduction of ESR1 and PIK3CA ctDNA in patients treated with GDC-0927. ER pathway suppression was observed at both the transcript and protein level confirming pharmacodynamic activity of the SERD.

Citation Format: Spoerke JM, Daemen A, Chang C-W, Giltnane J, Metcalfe C, Dickler MN, Bardia A, Perez Fidalgo JA, Mayer IA, Boni V, Winer EP, Hamilton EP, Bellet M, Urruticoechea A, Gonzalez Martin A, Cortes J, Martin M, Gates M, Cheeti S, Fredrickson J, Wang X, Friedman LS, Liu L, Li R, Chan IT, Mueller L, Milan S, Lauchle J, Humke EW, Lackner MR. Phamacodynamic and circulating tumor DNA evaluation in a phase I study of GDC-0927, a selective estrogen receptor antagonist/ degrader (SERD) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-11-01.