Abstract P5-19-05: Health-related quality of life during a phase 2 study of talazoparib in patients with advanced breast cancer and germline BRCA1/2 mutations (ABRAZO)

Background: Talazoparib (TALA; 1 mg/d) was well tolerated and exhibited promising antitumor activity in ABRAZO, a 2-cohort, 2-stage, open-label phase 2 study (NCT02034916) in patients (pts) with locally advanced or metastatic breast cancer and gBRCA1/2 mutations following platinum-based therapy (cohort 1 [C1]) or ≥3 platinum-free cytotoxic-based regimens (cohort 2 [C2]). This analysis evaluates health-related quality of life (QoL) for both cohorts.

Methods: QoL was assessed on day 1 (baseline) and every 6 weeks for the initial 24 weeks and every 12 weeks thereafter, or sooner if progression was clinically suspected, using the EORTC QLQ-C30 and its breast cancer module, QLQ-BR23. For all scales, results were summarized using descriptive statistics for each cohort and at each time point, based on Characters (max 3400 including title, body and table [including spaces]): 3363 No abbreviations in title; title sentence case; define acronyms; no figures Category: Psychosocial, QOL, and Educational Aspects – Other 2 observed values and changes from baseline (clinically meaningful defined as ≥10-point change from baseline). Time to deterioration (TTD; defined as ≥10-point decrease in global health status [GHS]/functional scales or increase in symptom scales) analyses using survival analysis methods were carried out on the GHS/functional scales of QLQ-C30 and symptom scales of QLQ-BR23.

Results:GHS was maintained from baseline across all time points for both C1 and C2 except at week 24 in C2, when a statistically significant but not clinically meaningful improvement in GHS was observed. In C1, statistically significant and clinically meaningful improvement was observed at specific time points in 4 functional scales (body image, week 6; sexual functioning, week 24; sexual enjoyment, week 36; and future perspective, weeks 6, 18, and 24) and in 3 symptom scales (dyspnea, week 24; insomnia, week 24; and breast symptoms, weeks 6 and 36). Statistically significant and clinically meaningful deterioration in C1 was observed in 2 functional scales (emotional functioning, week 12 and end of treatment, and role functioning, end of treatment) and in 1 symptom scale (fatigue, week 6). In C2, statistically significant and clinically meaningful improvement was observed at specific time points in 4 functional scales (role functioning, week 24; social functioning, week 24; sexual enjoyment, week 18; and future perspective, weeks 6, 12, and 18) and in 5 symptom scales (nausea/vomiting, week 18; pain, weeks 12, 18, and 24; insomnia, week 24; breast symptoms, weeks 12 and 18; and arm symptoms, week 48). For C2, no statistically significant and clinically meaningful deterioration was observed for any functional or symptoms scales across all time points, except in the dyspnea symptom scale at week 18. For C1 and C2, the median (95% confidence interval) TTD of GHS was 2.8 (2.1-3.0) and 5.5 (4.2-5.7) months, respectively. The median TTD for all QLQ-C30 functional scales for C1 and C2 ranged 2.1-3.1 and 4.2-5.6 months, respectively; the median TTD for all QLQ-BR23 symptoms scales ranged 2.6-4.0 and 4.2-5.6 months, respectively.

Conclusions: The QoL of TALA-treated patients during ABRAZO was maintained. QoL is being evaluated among atients with germline BRCA1/2 mutated advanced BC treated with TALA vs physician's choice chemotherapy in the phase 3 EMBRACA trial (NCT01945775).

Citation Format: Hurvitz SA, Turner NC, Telli ML, Rugo HS, Mailliez A, Ettl J, Grischke E-M, Mina LA, Balmaña J, Fasching PA, Tudor C, Quek RGW, Hannah AL, Robson ME, Wardley AM. Health-related quality of life during a phase 2 study of talazoparib in patients with advanced breast cancer and germline BRCA1/2 mutations (ABRAZO) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-19-05.

Abstract P1-14-03: ABRAZO: Exposure-efficacy and -safety analyses of breast cancer patients with germline BRCA1/2 mutations receiving talazoparib in a phase 2 open-label trial

Background: Talazoparib (TALA) is a dual-mechanism poly (ADP-ribose) polymerase (PARP) inhibitor that traps PARP on DNA. Efficacy results of this phase 2 trial were previously presented (Turner et al, ASCO 2017, abstract 1007). This study included sparse pharmacokinetic (PK) sampling for patients through cycle 4 of therapy. Exploratory analyses included assessment of exposure versus parameters of efficacy and safety.

Methods: ABRAZO (NCT02034916) was a parallel-cohort, open-label phase 2 study of TALA (1 mg/d) following (i) platinum-based therapy (cohort 1) or (ii) ≥3 platinum-free cytotoxic-based regimens (cohort 2) in patients with locally advanced or metastatic breast cancer and germline BRCA1/2 mutation. Sparse PK sampling was performed on day 1 of cycles 1-4, consisting of a predose sample collected ≤60 minutes prior to dosing and 2 postdose samples collected ≥30 minutes after dosing (time of food ingestion prior to the dose was collected). The collection times of the 2 postdose samples were separated by ≥2 hours. Efficacy parameters included radiographic progression-free survival (rPFS) by central review and objective response rate (ORR). Safety parameters included incidence of overall adverse events (AEs) and grade ≥3 AEs. Individual AUCs (area under concentration-time curves) for exposure-response analyses were predicted by population PK analyses.

Results: Patients were divided into AUC tertiles: low (median, 109.0 ng*hr/mL; n=27), intermediate (median, 170.8 ng*hr/mL; n=27), and high (median, 219.2 ng*hr/mL; n=27). Median rPFS was 5.3 months (95% confidence interval [CI], 3.1, 8.3) in the lowest AUC tertile, 5.6 months (95% CI, 3.7, 8.4) in the intermediate AUC tertile, and 5.3 months (95% CI, 3.9, 5.6) in the highest AUC tertile. The ORR was 22.2% (95% CI, 8.6, 42.3) in the lowest AUC tertile, 25.9% (95% CI, 11.1, 46.3) in the intermediate AUC tertile, and 37.0% (95% CI, 19.4, 57.6) in the highest AUC tertile. AEs of any grade were reported in 11 patients (40.7%) in the lowest AUC tertile, 21 patients (77.8%) in the intermediate AUC tertile, and 22 patients (81.5%) in the highest AUC tertile. Grade ≥3 AEs were reported in 8 patients (29.6%) in the lowest AUC tertile and in 18 patients (66.7%) in the intermediate and highest AUC tertiles. The most common AEs in all 3 exposure tertiles were anemia, thrombocytopenia, and neutropenia.

Conclusions: Median rPFS did not change with increasing systemic exposure. There may be a trend to higher ORR in patients with highest systemic exposure. A larger percentage of patients experienced AEs with elevated systemic exposure. Increased response rates with greater exposure does not translate to improved rPFS. These results should be interpreted with caution due to the low patient numbers in each cohort.

Citation Format: Telli ML, Turner NC, Mailliez A, Ettl J, Grischke E-M, Mina LA, Balmaña J, Hurvitz SA, Wardley AM, Fasching PA, Tudor C, Nguyen L, Hannah AL, Robson ME, Rugo HS. ABRAZO: Exposure-efficacy and -safety analyses of breast cancer patients with germline BRCA1/2 mutations receiving talazoparib in a phase 2 open-label trial [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-14-03.

Abstract OI-1: Tackling Breast Cancer Diversity

Breast cancer is a highly diverse disease with multiple subtypes and driver mutations. Further diversity may develop, particularly in metastatic breast cancer, due to the selective pressure of treatment. In ER positive breast cancer, activating mutations of the oestrogen receptor (ESR1), along with mutations in the NF1, KRAS and FGFR genes, are all enriched in endocrine resistant breast cancer, although rare in untreated primary breast cancer.

This diversity presents a substantial challenge to the treatment of metastatic breast cancer, with new therapeutic approaches required to tackle this heterogeneity. Circulating tumour DNA analysis, to identify selected mutations in the tumour and guide matching targeted therapy, has preliminary evidence of clinical utility. Targeting common phenotypes presents an alterative therapeutic approach, targeting the dependence of luminal breast cancer on CDK4/6 to initiate cell cycle entry. Pre-clinical evidence supports combining CDK4/6 inhibition with mutation-targeted therapies, although implementing these combinations presents a substantial clinical translational challenge.

A novel approach to overcoming tumour heterogeneity is to identify and target micro-metastatic cancer in the adjuvant setting. Micro-metastatic cancer can be detected with highly sensitive circulating tumour DNA analysis for minimal residual disease (MRD) detection. This may open up a new paradigm of treatment guided by MRD monitoring, potentially treating cancer in a setting where the cancer may be less genetically diverse, with lower potential to develop resistance to therapy.

Citation Format: Turner NC. Tackling Breast Cancer Diversity [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OI-1.

Abstract P2-02-01: Withdrawn

This abstract was withdrawn by the authors.

Assessing HER2 Amplification in Plasma cfDNA

Digital PCR (dPCR) is a highly accurate method to determine DNA concentration. In dPCR, DNA is portioned into many discrete single entities, and these are analyzed individually for the presence or absence of a target molecule of interest. Here we describe how digital PCR can be employed to determine the presence of oncogenic amplification through noninvasive analysis of circulating free DNA (cfDNA), and exemplify this approach by developing a plasma circulating free DNA dPCR assay for HER2 copy number.

CDK4/6 Inhibitors: Promising Opportunities beyond Breast Cancer

Patnaik and colleagues report on the safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of abemaciclib for the treatment of advanced solid cancers, demonstrating antitumor activity in advanced breast cancers as well as glioblastoma, melanoma, non-small cell lung cancer, colorectal cancer, and ovarian cancer. The development of abemaciclib and other CDK4/6 inhibitors should now be fully optimized through the use of novel predictive biomarkers of response and rational combinations. Cancer Discov; 6(7); 697-9. ©2016 AACRSee related article by Patnaik et al., p. 740.

Diverse BRCA1 and BRCA2 Reversion Mutations in Circulating Cell-Free DNA of Therapy-Resistant Breast or Ovarian Cancer

Purpose: Resistance to platinum-based chemotherapy or PARP inhibition in germline BRCA1 or BRCA2 mutation carriers may occur through somatic reversion mutations or intragenic deletions that restore BRCA1 or BRCA2 function. We assessed whether BRCA1/2 reversion mutations could be identified in circulating cell-free DNA (cfDNA) of patients with ovarian or breast cancer previously treated with platinum and/or PARP inhibitors.Experimental Design: cfDNA from 24 prospectively accrued patients with germline BRCA1 or BRCA2 mutations, including 19 patients with platinum-resistant/refractory ovarian cancer and five patients with platinum and/or PARP inhibitor pretreated metastatic breast cancer, was subjected to massively parallel sequencing targeting all exons of 141 genes and all exons and introns of BRCA1 and BRCA2 Functional studies were performed to assess the impact of the putative BRCA1/2 reversion mutations on BRCA1/2 function.Results: Diverse and often polyclonal putative BRCA1 or BRCA2 reversion mutations were identified in cfDNA from four patients with ovarian cancer (21%) and from two patients with breast cancer (40%). BRCA2 reversion mutations were detected in cfDNA prior to PARP inhibitor treatment in a patient with breast cancer who did not respond to treatment and were enriched in plasma samples after PARP inhibitor therapy. Foci formation and immunoprecipitation assays suggest that a subset of the putative reversion mutations restored BRCA1/2 function.Conclusions: Putative BRCA1/2 reversion mutations can be detected by cfDNA sequencing analysis in patients with ovarian and breast cancer. Our findings warrant further investigation of cfDNA sequencing to identify putative BRCA1/2 reversion mutations and to aid the selection of patients for PARP inhibition therapy. Clin Cancer Res; 23(21); 6708-20. ©2017 AACR.

Single-Cell Dynamics Determines Response to CDK4/6 Inhibition in Triple-Negative Breast Cancer

Purpose: Triple-negative breast cancer (TNBC) is a heterogeneous subgroup of breast cancer that is associated with a poor prognosis. We evaluated the activity of CDK4/6 inhibitors across the TNBC subtypes and investigated mechanisms of sensitivity.Experimental Design: A panel of cell lines representative of TNBC was tested for in vitro and in vivo sensitivity to CDK4/6 inhibition. A fluorescent CDK2 activity reporter was used for single-cell analysis in conjunction with time-lapse imaging.Results: The luminal androgen receptor (LAR) subtype of TNBC was highly sensitive to CDK4/6 inhibition both in vitro (P < 0.001 LAR vs. basal-like) and in vivo in MDA-MB-453 LAR cell line xenografts. Single-cell analysis of CDK2 activity demonstrated differences in cell-cycle dynamics between LAR and basal-like cells. Palbociclib-sensitive LAR cells exit mitosis with low levels of CDK2 activity, into a quiescent state that requires CDK4/6 activity for cell-cycle reentry. Palbociclib-resistant basal-like cells exit mitosis directly into a proliferative state, with high levels of CDK2 activity, bypassing the restriction point and the requirement for CDK4/6 activity. High CDK2 activity after mitosis is driven by temporal deregulation of cyclin E1 expression. CDK4/6 inhibitors were synergistic with PI3 kinase inhibitors in PIK3CA-mutant TNBC cell lines, extending CDK4/6 inhibitor sensitivity to additional TNBC subtypes.Conclusions: Cell-cycle dynamics determine the response to CDK4/6 inhibition in TNBC. CDK4/6 inhibitors, alone and in combination, are a novel therapeutic strategy for specific subgroups of TNBC. Clin Cancer Res; 23(18); 5561-72. ©2017 AACR.

Modeling Therapy Resistance in BRCA1/2-Mutant Cancers

Although PARP inhibitors target BRCA1- or BRCA2-mutant tumor cells, drug resistance is a problem. PARP inhibitor resistance is sometimes associated with the presence of secondary or "revertant" mutations in BRCA1 or BRCA2 Whether secondary mutant tumor cells are selected for in a Darwinian fashion by treatment is unclear. Furthermore, how PARP inhibitor resistance might be therapeutically targeted is also poorly understood. Using CRISPR mutagenesis, we generated isogenic tumor cell models with secondary BRCA1 or BRCA2 mutations. Using these in heterogeneous in vitro culture or in vivo xenograft experiments in which the clonal composition of tumor cell populations in response to therapy was monitored, we established that PARP inhibitor or platinum salt exposure selects for secondary mutant clones in a Darwinian fashion, with the periodicity of PARP inhibitor administration and the pretreatment frequency of secondary mutant tumor cells influencing the eventual clonal composition of the tumor cell population. In xenograft studies, the presence of secondary mutant cells in tumors impaired the therapeutic effect of a clinical PARP inhibitor. However, we found that both PARP inhibitor-sensitive and PARP inhibitor-resistant BRCA2 mutant tumor cells were sensitive to AZD-1775, a WEE1 kinase inhibitor. In mice carrying heterogeneous tumors, AZD-1775 delivered a greater therapeutic benefit than olaparib treatment. This suggests that despite the restoration of some BRCA1 or BRCA2 gene function in "revertant" tumor cells, vulnerabilities still exist that could be therapeutically exploited. Mol Cancer Ther; 16(9); 2022-34. ©2017 AACR.

Diverse BRCA1 and BRCA2 Reversion Mutations in Circulating Cell-Free DNA of Therapy-Resistant Breast or Ovarian Cancer

Purpose: Resistance to platinum-based chemotherapy or PARP inhibition in germline BRCA1 or BRCA2 mutation carriers may occur through somatic reversion mutations or intragenic deletions that restore BRCA1 or BRCA2 function. We assessed whether BRCA1/2 reversion mutations could be identified in circulating cell-free DNA (cfDNA) of patients with ovarian or breast cancer previously treated with platinum and/or PARP inhibitors.Experimental Design: cfDNA from 24 prospectively accrued patients with germline BRCA1 or BRCA2 mutations, including 19 patients with platinum-resistant/refractory ovarian cancer and five patients with platinum and/or PARP inhibitor pretreated metastatic breast cancer, was subjected to massively parallel sequencing targeting all exons of 141 genes and all exons and introns of BRCA1 and BRCA2 Functional studies were performed to assess the impact of the putative BRCA1/2 reversion mutations on BRCA1/2 function.Results: Diverse and often polyclonal putative BRCA1 or BRCA2 reversion mutations were identified in cfDNA from four patients with ovarian cancer (21%) and from two patients with breast cancer (40%). BRCA2 reversion mutations were detected in cfDNA prior to PARP inhibitor treatment in a patient with breast cancer who did not respond to treatment and were enriched in plasma samples after PARP inhibitor therapy. Foci formation and immunoprecipitation assays suggest that a subset of the putative reversion mutations restored BRCA1/2 function.Conclusions: Putative BRCA1/2 reversion mutations can be detected by cfDNA sequencing analysis in patients with ovarian and breast cancer. Our findings warrant further investigation of cfDNA sequencing to identify putative BRCA1/2 reversion mutations and to aid the selection of patients for PARP inhibition therapy. Clin Cancer Res; 23(21); 6708-20. ©2017 AACR.

Palbociclib Combined with Fulvestrant in Premenopausal Women with Advanced Breast Cancer and Prior Progression on Endocrine Therapy: PALOMA-3 Results

BACKGROUND

The efficacy and safety of palbociclib, a cyclin-dependent kinase 4/6 inhibitor, combined with fulvestrant and goserelin was assessed in premenopausal women with advanced breast cancer (ABC) who had progressed on prior endocrine therapy (ET).

PATIENTS AND METHODS

One hundred eight premenopausal endocrine-refractory women ≥18 years with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) ABC were among 521 women randomized 2:1 (347:174) to fulvestrant (500 mg) ± goserelin with either palbociclib (125 mg/day orally, 3 weeks on, 1 week off) or placebo. This analysis assessed whether the overall tolerable safety profile and significant progression-free survival (PFS) improvement extended to premenopausal women. Potential drug-drug interactions (DDIs) and ovarian suppression with goserelin were assessed via plasma pharmacokinetics and biochemical analyses, respectively. (ClinicalTrials.gov identifier: NCT01942135) RESULTS: Median PFS for premenopausal women in the palbociclib (n = 72) versus placebo arm (n = 36) was 9.5 versus 5.6 months, respectively (hazard ratio, 0.50, 95% confidence interval: 0.29-0.87), and consistent with the significant PFS improvement in the same arms for postmenopausal women. Any-grade and grade ≤3 neutropenia, leukopenia, and infections were among the most frequent adverse events reported in the palbociclib arm with concurrent goserelin administration. Hormone concentrations were similar between treatment arms and confirmed sustained ovarian suppression. Clinically relevant DDIs were not observed.

CONCLUSION

Palbociclib combined with fulvestrant and goserelin was an effective and well-tolerated treatment for premenopausal women with prior endocrine-resistant HR+/HER2- ABC. Inclusion of both premenopausal and postmenopausal women in pivotal combination ET trials facilitates access to novel drugs for young women and should be considered as a new standard for clinical trial design.

IMPLICATIONS FOR PRACTICE

PALOMA-3, the first registrational study to include premenopausal women in a trial investigating a CDK4/6 inhibitor combined with endocrine therapy, has the largest premenopausal cohort reported in an endocrine-resistant setting. In pretreated premenopausal women with hormone receptor-positive advanced breast cancer, palbociclib plus fulvestrant and goserelin (luteinizing hormone-releasing hormone [LHRH] agonist) treatment almost doubled median progression-free survival (PFS) and significantly increased the objective response rate versus endocrine monotherapy, achieving results comparable to those reported for chemotherapy without apparently interfering with LHRH agonist-induced ovarian suppression. The significant PFS gain and tolerable safety profile strongly support use of this regimen in premenopausal women with endocrine-resistant disease who could possibly delay chemotherapy.

Advances in the treatment of advanced oestrogen-receptor-positive breast cancer

Oestrogen-receptor-positive breast cancer is the most common subtype of breast cancer. Endocrine therapies that target the dependence of this subtype on the oestrogen receptor have substantial activity, yet the development of resistance to therapy is inevitable in advanced cancer. Major progress has been made in identifying the drivers of oestrogen-receptor-positive breast cancer and the mechanisms of resistance to endocrine therapy. This progress has translated into major advances in the treatment of advanced breast cancer, with several targeted therapies that enhance the efficacy of endocrine therapy; inhibitors of mTOR and inhibitors of the cyclin-dependent kinases CDK4 and CDK6 substantially improve progression-free survival. A new wave of targeted therapies is being developed, including inhibitors of PI3K, AKT, and HER2, and a new generation of oestrogen-receptor degraders. Considerable challenges remain in patient selection, deciding on the most appropriate order in which to administer therapies, and establishing whether cross-resistance occurs between therapies.

Experience of implementing a novel random sampling BICR audit for investigator (INV)-assessed progression-free survival (PFS) in the PALOMA-3 trial

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Background: PFS has frequently been used as a primary endpoint for evaluating efficacy of anticancer therapies in randomized clinical trials. Given high correlation between INV and independent (BICR) assessments with respect to the relative treatment effect, a pre-planned BICR audit of INV progression assessment in a random subgroup of patients (pts) instead of a BICR review of all progression assessments can be an acceptable approach to verify the INV assessments and to evaluate the potential bias in INV PFS results. Methods: PALOMA-3 was a randomized, double blind, placebo (PCB) controlled, Ph 3 study with the primary objective of demonstrating the superiority of palbociclib (PAL) + fulvestrant (F) over PCB + F in women with HR+, HER2- metastatic breast cancer (MBC). The primary endpoint was INV assessed PFS. BICR assessment of PFS was performed with the use of a novel audit approach involving a random sample–based BICR to verify if the INV assessed PFS was accurate. A third-party core imaging laboratory performed the blinded review for a randomly selected subgroup of pts (~40%). NIH and PhRMA methods were used to evaluate the potential for bias in the INV PFS results. Results: PAL + F improved PFS in patients with HR+, HER2- MBC. The observed INV HR was 0.46 (95% CI: 0.36, 0.59; stratified 1-sided p < 0.0001) in favor of PAL + F. The median PFS was 9.5 mo (95% CI: 9.2, 11.0) in the PAL + F arm and 4.6 mo (95% CI: 3.5, 5.6) in the PCB + F arm (Lancet Oncol. 2016; 17: 425–39). The estimated HR of the complete BICR data incorporating the information from the complete INV assessed PFS and the random sample audited BICR subgroup was 0.33 with the upper bound of the 1-sided 95% CI of 0.47. The results confirmed the INV assessed treatment effect and detected no INV bias in favor of PAL + F. Conclusions: PALOMA-3 is the first registrational trial to use a BICR audit and has received positive reviews from regulatory agencies. The experience of implementing the random sampling BICR audit in PALOMA-3 demonstrates that this approach can be used for randomized, double blind oncology trials with solid tumors where INV assessed PFS is the primary endpoint and a large treatment effect is targeted. Sponsor: Pfizer. Clinical trial information: NCT01942135.

Tracking evolution of aromatase inhibitor resistance with circulating tumour DNA (ctDNA) in metastatic breast cancer

1015

Background: Selection of resistance mutations may play a major role in the development of endocrine resistance. ESR1 mutations are rare in primary breast cancer but have a high prevalence in patients treated with aromatase inhibitors (AI) for advanced breast cancer. We investigated the evolution of genetic resistance to first line AI therapy using sequential ctDNA sampling in patients with advanced breast cancer. Methods: Seventy-one patients on first line AI therapy for metastatic breast cancer were enrolled in a prospective study to collect plasma samples for ctDNA analysis every three months on therapy, and at disease progression. All plasma samples were analysed with ESR1 multiplex digital PCR assays, and samples at disease progression were analysed by InVision (enhanced tagged-amplicon sequencing). Mutations were tracked back through samples prior to disease progression to study the evolution of mutations on therapy. Results: Of the 34 patients who progressed on first line AI, 53% (18/34) had ESR1 mutations detectable at progression. Sequencing of progression plasma ctDNA identified polyclonal RAS mutations in 10.7% (3/28) progressing patients (2 polyclonal KRAS, 1 monoclonal HRAS), all of whom also had ESR1 mutations, and a patient with an activating p.R248C FGFR3 mutation. ESR1 mutations were subclonal in 78.6% (11/14) patients, with all RAS mutations being rare subclones. In serial tracking prior to progression, ESR1 mutations were detectable in plasma with a median of 5.3 months (95% CI 2.9-NA) prior to clinical progression. Conclusions: ESR1 mutations are found at high frequency in patients progressing on AI, but are frequently sub-clonal and may not be the sole driver of AI resistance in these patients. Poly-clonal KRAS mutations are identified as a novel mechanism of resistance to AI, associated with detection of ESR1 mutations.

Final results of a phase 2 study of talazoparib (TALA) following platinum or multiple cytotoxic regimens in advanced breast cancer patients (pts) with germline BRCA1/2 mutations (ABRAZO)

1007

Background: TALA is a dual-mechanism PARP inhibitor that traps PARP on DNA. This study was designed to assess the activity of TALA in pts with g BRCA1/2mutation previously exposed to platinum or multiple prior cytotoxic regimens. Methods: ABRAZO (NCT02034916) is a 2-cohort, 2-stage phase 2 study of TALA (1 mg/d) following platinum-based therapy (Cohort 1 [C1]) or ≥ 3 platinum-free cytotoxic-based regimens (Cohort 2 [C2]) in pts with locally advanced or metastatic breast cancer (MBC) and g BRCA1/2mutation. Pts had ECOG PS ≤ 1 and measurable disease by RECIST v1.1. Five responses per cohort were required in ≤ 35 pts to progress to stage 2. The primary endpoint was confirmed ORR by independent radiology facility (IRF). Secondary endpoints: clinical benefit rate ≥ 24 weeks (CBR24), DOR, PFS, and OS. Results: From May 2014 to Feb 2016, 84 pts were enrolled (C1, n = 49; C2, n = 35). At data cutoff (1 Sep 2016), 9 pts continued on treatment. Both cohorts proceeded to stage 2 before enrollment closed. Median age was 50 (range, 31–75) years; 58% of pts had an ECOG PS of 0. TNBC/HR+ incidence in C1 and C2 was 59%/41% and 17%/83%, respectively. Median number of prior cytotoxic regimens administered for advanced disease was 2 in C1 and 4 in C2. ORR by IRF for BRCA1/BRCA2 was 24%/34%, and ORR by IRF for TNBC/HR+ was 26%/29%. Common all grade AEs: anemia (52%), fatigue (45%), nausea (42%), diarrhea (33%), thrombocytopenia (33%), and neutropenia (27%). Grade ≥ 3 AEs: anemia (35%), thrombocytopenia (19%), and neutropenia (15%). Nonhematological AEs grade ≥ 3 did not occur. AEs related to TALA led to drug discontinuation in 3 pts (4%); 4 AEs resulted in death, none related to TALA. Conclusions: TALA was well tolerated in MBC pts with a g BRCA1/2 mutation, exhibiting promising antitumor activity in C1 and C2. TALA vs physician’s choice of treatment in g BRCA1/2-mutated MBC is being evaluated in the phase 3 EMBRACA trial (NCT01945775). Clinical trial information: NCT02034916. [Table: see text]

Palbociclib exposure-response analyses in second-line treatment of hormone-receptor positive advanced breast cancer (ABC)

1053

Background: Palbociclib (PAL) is an oral inhibitor of cyclin-dependent kinases 4 and 6 approved for ABC. Exposure-response analyses for efficacy and safety endpoints were performed to evaluate the current PAL clinical dosing regimen (125 mg daily, 3 weeks on and 1 week off) and dose modification strategy in 2nd-line ABC. Methods: The present analyses used data from PALOMA3, a phase 3 study comparing the safety and efficacy of fulvestrant plus either PAL or placebo in 2nd-line ABC patients (PTs). A Bayesian pharmacokinetic (PK) analysis was conducted to estimate PAL PK parameters for individual PTs. Average concentration of PAL over the entire treatment (Cavg) was derived from average daily dose intensity divided by post hoc estimates of clearance for each PT. Time varying Cavg (Cavgt) was also derived to account for dose modifications up to each observation point. Kaplan-Meier method and the Cox proportional hazards model were employed to explore relationship between progression-free survival (PFS) and Cavg, Cavgt, as well as other prognostic factors. A semi-mechanistic PK-pharmacodynamic (PD) model was built to quantify the relationship between PAL concentration and absolute neutrophil count (ANC). Results: The median PFS for low and high PAL exposure groups divided according to Cavg were similar (9.47 and 10.9 months, respectively) and significantly higher than that of the control arm (4.57 months). While Cavgtwas found to be a significant predictor for PFS in univariate analysis (P-value < 0.05), this relationship was not significant in the multivariate analysis where other significant prognostic factors were also included. The PK-PD analysis for safety endpoint indicated higher PAL concentrations were associated with lower ANC, which is consistent with the fact that ANC profiles were well managed by dose modification strategies, i.e., dose interruption, delay and reduction. Conclusions: The analysis results suggested PTs were benefited similarly from fulvestrant plus PAL treatment with manageable safety profile, supporting a favorable benefit-risk profile of PAL under the current dosing regimen and dose modification strategy in 2nd-line ABC. Funding: Pfizer Inc. Clinical trial information: NCT01942135.

Predictors of prolonged benefit from palbociclib (PAL) plus fulvestrant (F) in women with endocrine-resistant hormone receptor–positive/human epidermal growth factor receptor 2–negative (HR+/HER2–) advanced breast cancer (ABC) in PALOMA-3

1050

Background: PAL+F improved progression-free survival (PFS) over F + placebo (P) in patients (pts) with endocrine-resistant HR+/HER2– ABC. We examined factors predictive of long-term benefit on PAL+F. Methods: Pre/postmenopausal pts with HR+/HER2– ABC that progressed on prior endocrine therapy (ET) were randomized 2:1 to PAL (125 mg/d oral [3 wk on, 1 wk off]) + F (500 mg) or P+F. Characteristics of pts with prolonged benefit (treatment [tx] duration ≥18 mo for PAL+F; ≥12 mo for P+F based on median PFS and tx duration) were compared with the intent-to-treat (ITT) population. Results: PAL+F improved PFS vs P+F (11.2 vs 4.6 mo; hazard ratio, 0.50). By Aug 2016, 138 pts had long-term benefit: 100/347 (29%) pts on PAL+F received tx for ≥18 mo, including 70 (20%) who received > 2 y (26–39 cycles). In contrast, 38/174 (22%) pts on P+F received ≥12 mo of tx; only 16 (9%) received > 2 y (27–38 cycles). No apparent differences in baseline characteristics of pts with long-term benefit were observed between groups except that a greater proportion of those on P+F had a single site of disease involvement (40% PAL+F vs 63% P+F). Pts with long-term benefit on PAL+F had lower rates of visceral disease (42% vs 60%), liver metastases (18% vs 40%), and ≥3 disease sites (27% vs 39%) at baseline vs the ITT population; no difference in sensitivity to prior ET was observed (84% vs 79%). Objective response rate (ORR) was higher among pts with prolonged benefit on PAL+F vs ITT (36% vs 26%). Conclusions: PAL+F is associated with prolonged benefit in about a third of pts treated with the combination in PALOMA-3. These pts achieve higher ORR compared to other study pts and the benefit is independent of baseline site and number of metastatic recurrences and prior endocrine sensitivity. Benefit from F alone is less prolonged and appears limited to those with 1 site of disease involvement. The analysis confirms the efficacy of PAL+F in HR+ ABC with visceral recurrence. Biomarker analyses are ongoing in pts with long-term benefit to understand molecular features predictive of tx sensitivity. Funding: Pfizer. Clinical trial information: NCT01942135.

A phase I trial of selective PI3K inhibitor taselisib (tas) plus palbociclib (palb) with and without endocrine therapy incorporating pharmacodynamic (PD) studies in patients (pts) with advanced cancers

2573

Background: The phosphatidylinositol 3-kinase (PI3K) pathway is commonly mutated in cancer. Tas is a selective β-isoform-sparing PI3K inhibitor with improved therapeutic index compared to pan-PI3K inhibitors. Palb is a CDK4/6 inhibitor now standard of care in combination with endocrine therapy (ET) in hormone receptor positive breast cancer. Combination of Tas, Palb and ET is synergistic in preclinical models. Methods: This investigator-initiated study investigated safety and tolerability, pharmacokinetics (PK), PD and antitumor activity of Tas+Palb, with addition of ET in dose expansion. Pts were enrolled in 3+3 dose escalation design. Tas was given continuously or 3-weeks-on, 1-week-off (3/1), Palb was given on 3/1 schedule. PD studies included analyses of platelet-rich plasma (PRP) (n = 20) and paired tumor biopsies (n = 5). Serial circulating tumor DNA was monitored in pts with PIK3CA mutations. Results: 24 pts were treated, 22 with Tas+Palb, 2 with Tas+Palb+fulvestrant(ful); M/F 11/13, median lines prior therapy 4. Treatment was well tolerated with mainly G1-2 toxicities. Most frequent G3 toxicities were neutropenia (5/24), thrombocytopenia (5/24) and rash (5/24), with no G4/5 toxicities. Two pts had dose-limiting toxicities (DLT) at DL2. No DLTs were observed at DL4, although pts experienced delayed neutrophil recovery. PK was linear and comparable with monotherapy. At 125mg Palb, significant decreases in pAKT and pGSK3β in PRP confirmed PI3K target inhibition. Two pts with PI3KCA H1047R mutant breast cancers have ongoing RECIST partial response; 1 pt with PIK3CA E542K colorectal cancer had stable disease for 20 weeks. Conclusions: Tas+Palb is well tolerated with evidence of PD and antitumor activity. Dose expansion including recruitment to triplet Tas+Palb+ful and Tas+Palb+letrozole is ongoing with continuous Tas 2mg QD, and Palb 100mg QD on 3/1 schedule, increasing to 125mg after cycle 1 in absence of myelosuppression. Clinical trial information: NCT02389842. [Table: see text]

Predicting response to radical (chemo)radiotherapy (R-CRT) with circulating HPV DNA and tumor DNA (ctDNA) analysis in locally-advanced head and neck squamous cell carcinoma (LAHNC)

6043

Background: Following R-CRT for human papilloma virus positive (HPV+) and negative (HPV-) LAHNC, patients frequently undergo unnecessary neck dissection (ND) and/or repeated biopsies for abnormal PET-CT findings even in the presence of a complete pathological response (pCR), which causes significant morbidity. We assessed the role of circulating tumor DNA analysis in identifying patients with true residual disease. Methods: We prospectively recruited development (DC, n=55) and test (TC, n=33) cohorts of LAHNC patients having R-CRT. For HPV+ tumors we developed a novel amplicon based next generation sequencing assay (HPV-detect) to detect circulating HPV DNA and for HPV- tumors we used personalised droplet digital PCR assays of somatic mutations. Circulating tumor DNA levels at 12 weeks post-R-CRT were correlated to residual disease assessed by PET-CT and surgery. Results: In the DC (27 HPV+), baseline HPV-detect demonstrated 100% sensitivity and 93% specificity, confirmed in the TC (20 HPV+). 37 HPV+ patients (DC&TC) had complete samples-set. 36 had a negative HPV-detect at end of treatment, including 6 patients who underwent ND (3) and repeat primary site biopsies (3) for positive PET-CT but had pCR on surgical/biopsy specimen. 1 patient had positive HPV-detect and positive biopsy, indicating 100% agreement for HPV-detect and residual cancer. In a 10 HPV- patients with complete sample-set, there was 90% agreement between ctDNA and residual disease in HPV- tumors (3 ctDNA positive and tumor present, 1 ctDNA negative but tumor present, and 6 negative ctDNA negative tumor) with 80% sensitivity for residual disease and 100% specificity. Combined agreement between ctDNA testing (HPV+ and -) & residual disease was 98% (Table). Conclusions: Circulating HPV DNA quantified using HPV-detect and ctDNA identifies patients with residual disease post-R-CRT in LAHNC. Further studies are required to validate these findings. [Table: see text]

Predicting sensitivity to palbociclib with early circulating tumor DNA dynamics in the PALOMA-3 trial

1018

Background: Palbociclib improves progression free survival (PFS) in patients with advanced, hormone receptor positive, HER2-negative breast cancer. There are currently no biomarkers to predict sensitivity to palbociclib. We investigated if early circulating tumour DNA (ctDNA) dynamics could predict clinical outcome on palbociclib (Palbo) and fulvestrant (F) in the PALOMA-3 trial. Methods: Plasma samples were prospectively collected in PALOMA-3 for ctDNA analysis at baseline, cycle 1 day 15 (D15) and end of treatment (EOT), and were screened for PIK3CA and ESR1 mutations using digital PCR. The primary objective was to assess whether early dynamic changes in PIK3CA mutations would predict PFS in patients treated with Palbo + F. Suppression of PIK3CA ctDNA levels below an optimised cut-off at cycle 1 D15, relative to baseline levels, was termed a ‘circulating DNA ratio (CDR) response. Results: PIK3CA mutations were identified in 22.0% (100/455) of screened baseline samples with 52 of these randomised to Palbo + F and having matched D15 samples. Patients on Palbo + F with a CDR response had a median PFS of 11.2 months (95%CI 11.1 – undefined) whereas patients on Palbo + F without a CDR response had a median PFS of 4.1 months (95%CI 3.6 – 5.5) (HR for no CDR response 4.92, 95% CI 1.98 – 12.26, p = 0.0002). Overall, Palbo + F suppressed D15 PIK3CA ctDNA levels to a greater extent than placebo + F (p<0.0001). ESR1 mutations were identified in 25.6% (114/445) of screened baseline samples, 65 having matched D15 samples. ESR1 mutations showed greater ctDNA suppression than PIK3CA mutations, and were more frequently undetectable at EOT (25.8% ESR1 undetectable 8/31, v 2.6% for PIK3CA, 1/38, p=0.004). Clearance of ESR1 mutation at EOT was associated with early loss of ESR1at D15 (p = 0.027). Conclusions: Early circulating tumor DNA assessment may predict sensitivity to palbociclib and fulvestrant, and if validated by further analysis may allow treatment to be adapted prior to progression. ESR1 mutations are frequently lost after treatment with palbociclib and fulvestrant.

Advances and challenges in targeting FGFR signalling in cancer

Fibroblast growth factors (FGFs) and their receptors (FGFRs) regulate numerous cellular processes. Deregulation of FGFR signalling is observed in a subset of many cancers, making activated FGFRs a highly promising potential therapeutic target supported by multiple preclinical studies. However, early-phase clinical trials have produced mixed results with FGFR-targeted cancer therapies, revealing substantial complexity to targeting aberrant FGFR signalling. In this Review, we discuss the increasing understanding of the differences between diverse mechanisms of oncogenic activation of FGFR, and the factors that determine response and resistance to FGFR targeting.

Abstract P4-22-03: Palbociclib in combination with endocrine therapy in treatment-naive and previously treated elderly women with HR+, HER2– advanced breast cancer: a pooled analysis from randomized phase 2 and 3 studies

Background: At least 40% of breast cancers are diagnosed in women ≥65 y old and most are hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-). Palbociclib (PAL) is an oral, small-molecule inhibitor of cyclin-dependent kinases 4 and 6. Randomized studies of PAL combined with endocrine therapy (ET) demonstrated significantly improved progression-free survival (PFS) in patients (pts) with treatment-naive and previously treated advanced breast cancer (ABC).

Methods: We evaluated the efficacy of PAL+ET vs ET alone in pts aged ≥65-74 and ≥75 y across multiple pivotal randomized phase 2 and 3 studies. Safety and pharmacokinetics (PK) data (blood samples collected from pts in phase 1/2 [PALOMA-1] and phase 1 studies [NCT00141297 and NCT00420056]) for PAL+ET were pooled and compared across age groups. Pts who had not received treatment for ABC were randomized to receive PAL+letrozole (LET) or LET alone/with placebo (PBO; PALOMA-1, open-label/PALOMA-2, double-blind). Pts who had progressed on prior ET were randomized to receive PAL+fulvestrant (FUL) or PBO+FUL (PALOMA-3, double-blind). The primary endpoint for these studies was investigator-assessed PFS. Safety assessments and blood counts occurred at baseline and every 2 weeks for the first 2 cycles and on day 1 of subsequent cycles.

Results: Among 872 pts treated with PAL+ET, 221 (25%) were aged ≥65-74 y and 83 (10%) were ≥75 y (PAL+LET: n=528, 162 and 56, respectively; PAL+FUL: n=347, 59 and 27). Median (range) treatment durations were 440 (1-1615) d, 502 (1-1615) d, and 459 (21-1404) d, respectively. Improvement in efficacy endpoints was seen with PAL+ET vs ET across all age groups (Table 1). Incidence of adverse events (AEs), serious AEs and discontinuations due to AEs were similar in the overall population (99%, 19%, 3%) and in pts aged ≥65-74 (99%, 25%, 5%) and ≥75 y (100%, 30%, 6%). Incidence of all grades and grade 3/4 neutropenia were also similar across age groups (overall: 67% and 54%; ≥65-74 y: 64% and 51%; ≥75 y: 77% and 60%). PK analysis showed no clinically relevant differences between arithmetic means, medians, and geometric means of the apparent oral clearance across age groups.

Conclusions: PAL in combination with ET is an effective and well-tolerated treatment option for elderly pts with HR+/HER2- endocrine-sensitive and -resistant ABC. A dose adjustment based on age is not required.

Sponsor: Pfizer

Table 1. PFS in pts ?65-74 and ?75 y (ITT populations)OverallAged ≥65-74 yAged ≥75 yPALOMA-1/PALOMA-2PAL+LET vs528 vs 303162 vs 9456 vs 26LET/LET+PBO,* nHR (95% CI);0.53 (0.44-0.64);0.66 (0.45-0.97);0.31 (0.16-0.61);1-sided P value&lt;0.00010.01620.0002Median PFS (95% CI), mo24.4 (22.0-26.2) vs27.5 (24.2-NR) vsNR (19.2-NR) vs13.6 (11.1-16.4)21.8 (16.3-31.3)10.9 (4.9-24.9)PALOMA-3PAL+FUL vs347 vs 17459 vs 3727 vs 6FUL+PBO, nHR (95% CI);0.46 (0.36-0.59);0.25 (0.14-0.45);0.87 (0.27-2.79);1-sided P value&lt;0.0001&lt;0.00010.4074Median PFS (95% CI), mo9.5 (9.2-11.0) vs16.1 (12.0-NR) vs13.6 (7.5-NR) vs4.6 (3.5-5.6)3.7 (1.9-5.3)7.4 (1.9-NR)HR=hazard ratio; ITT=intent to treat; NR=not reached. *Does not include 5 pts from phase 1 of PALOMA-1.

Citation Format: Rugo HS, Turner NC, Finn RS, Joy AA, Verma S, Harbeck N, Moulder S, Masuda N, Im Y-H, Zhang K, Kim S, Sun W, Schnell P, Huang-Bartlett C, Slamon D. Palbociclib in combination with endocrine therapy in treatment-naive and previously treated elderly women with HR+, HER2– advanced breast cancer: a pooled analysis from randomized phase 2 and 3 studies [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-22-03.

Abstract P1-02-01: Circulating tumor DNA analysis to predict relapse and overall survival in early breast cancer – Longer follow-up of a proof-of-principle study

Background

In a previous proof-of-principle study we demonstrated that detection of circulating tumour DNA (ctDNA) in the adjuvant setting, after completion of surgery and chemotherapy for early stage breast cancer, was associated with a high risk of early relapse. Here we present longer follow-up of the same series, to define the predictive power of ctDNA analysis for disease free survival, and assess the potential to predict overall survival.

Methods

We recruited a cohort of 55 women presenting with early stage, primary breast cancer, who were all scheduled to receive neo-adjuvant chemotherapy. The primary tumour was sequenced to identify somatic mutations, identifying at least one mutation in 43 patients. Mutations were tracked with digital PCR to identify ctDNA, in plasma samples taken either at a single post-surgical time point (2-6 weeks post-surgery) or with serial plasma samples taken every 6 months in the adjuvant setting.

Results

At a median 31.7 months follow-up, 42% (18/43) patients had relapsed. Detection of ctDNA at the single post-surgical time point was associated with poor disease free survival, HR=13.6 95%CI (4.5, 41.2) p&lt;0.001, and overall survival HR=84.7 95%CI (9.8, 730.4) p&lt;0.001. All patients with ctDNA detected in a single post-surgical time point relapsed and died in the follow-up period (7/7, 100% specificity), although the single post-surgery time point had modest 39% (7/18) sensitivity for relapse. Detection of ctDNA at any point in serial sampling was associated with poor disease free survival HR=25.7 95%CI (8.3, 79.8) p&lt;0.001 and overall survival HR=47.1 95%CI (6.1, 366.1) p&lt;0.001. All patients with ctDNA detected in a serial mutation tracking relapsed in the follow-up period (14/14, 100% specificity), with 78% (14/18) sensitivity for relapse. Sensitivity was limited by 3 cases of brain only relapse and one case of solitary ovarian relapse. Detection of ctDNA in serial sampling had a median lead-time of 8.1 months over clinical relapse.

Conclusion

Detection of ctDNA in the adjuvant setting has a high predictive power for future relapse and death from breast cancer. Therapeutic trials are required to determine whether mutation tracking identifies relapse sufficiently early to allow for further adjuvant therapy.

Citation Format: Turner NC, Garcia-Murillas I, Chopra N, Beaney M, Kilburn L, Cutts R, Osin P, Nerurkar A, Schiavon G, Hrebien S, Bliss J, Dowsett M, Smith I. Circulating tumor DNA analysis to predict relapse and overall survival in early breast cancer – Longer follow-up of a proof-of-principle study [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-02-01.

Abstract ES7-2: ES7-2 Mechanisms of resistant to therapy in ER positive cancer

Recent years have seen substantial advances in our understanding of ER positive/ HER2 negative breast cancer, both in the genetics of this subtype of breast cancer and the biological processes the drive tumor growth and resistance to therapy. Diverse targetable mutations have been identified in studies of primary breast cancer, along with acquired mutations in the estrogen receptor (ESR1) found in 30% of advanced breast cancers that progress on aromatase inhibitors. The therapeutic significance of this genetic diversity is being explored in ongoing studies. Therapies that target mTOR and CDK4/6 have entered routine clinical practice, demonstrating substantial improvements in progression free survival for patients with advanced cancer. The ongoing challenge is to identify biomarkers of sensitivity, to assist in selecting patients who benefit, and identify mechanisms of resistance to therapy to identify the optimal schedule of therapies and identify novel therapeutic approaches for resistant disease.

Citation Format: Turner NC. ES7-2 Mechanisms of resistant to therapy in ER positive cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr ES7-2.

Abstract P4-22-07: Long-term safety of palbociclib in combination with endocrine therapy in treatment-naive and previously treated women with HR+ HER2– advanced breast cancer: A pooled analysis from randomized phase 2 and 3 studies

Background: Palbociclib (PAL) is a selective and reversible oral cyclin-dependent kinase 4 and 6 inhibitor. Large randomized phase (ph) 2 and 3 trials showed significant improvement in progression-free survival (PFS) when PAL was combined with endocrine therapy (ET) vs ET alone in treatment (trt)-naive and previously treated hormone receptor?positive human epidermal growth factor receptor 2?negative (HR+ HER2–) advanced breast cancer (ABC) patients (pts). The median PFS with PAL+ET is &gt;2 years as a first-line therapy for ABC and 11.2 mo in endocrine-resistant ABC. We evaluated the long-term safety in PALOMA-1, -2, and -3.

Methods: We analyzed the tolerability of PAL in combination with ET in 3 randomized trials. Pts untreated for ABC were randomized to receive PAL+letrozole (LET) vs LET alone in PALOMA-1 (ph 2, open-label; 1:1) or randomized to receive PAL+LET vs placebo (PBO)+LET in PALOMA-2 (ph 3, double-blind; 2:1). PALOMA-3 included pts who progressed on prior ET, randomized to receive PAL+fulvestrant (FUL) or PBO+FUL (ph 3, double-blind; 2:1). Safety assessments, including a complete blood count, were done at baseline, on D1 of each cycle, and on D14 of the first 2 cycles. We evaluated adverse events (AEs) by 6-mo intervals (out to 36 mo) and cumulatively (12-, 24-, and 36-mo time points), and assessed latency (event onset) of pertinent adverse drug reactions (ADRs) in all pts treated in PALOMA-1, -2, and -3.

Results: A total of 1352 pts were pooled for this analysis; 872 pts received PAL+ET (527 pts, PAL+LET; 345 pts, PAL+FUL). Median duration of trt was 421 days in PALOMA-1 (January 2015), 603 days in PALOMA-2 (February 2016), and 330 days in PALOMA-3 (July 2015). PAL+LET was received by 119 pts as first-line trt in PALOMA-1 and 2 for 24–&lt;30 months and 11 pts were treated for &gt;36 mo. PAL+FUL was received by 140 pts for &gt;12 mo as second-line trt in PALOMA-3. The most commonly reported ADRs across all studies were neutropenia, fatigue, nausea, anemia, and leukopenia. The 6-mo-interval analyses of the most common (&gt;15%) AEs (by preferred term [PT]) from PALOMA-1, -2, and -3 indicated that these AEs were reported with the highest frequency during the first 6-mo interval and typically decreased in incidence over time to 30–&lt;36-mo; the most common hematologic AEs (clustered PTs) are shown (Table). The cumulative incidence of AEs after the first vs the second and third years showed similar frequencies of most AEs, including the most common ADRs.

Conclusions: Based on these long-term safety analyses, there is no evidence of specific cumulative or delayed toxicity resulting from prolonged trt with PAL+ET for HR+ HER2– ABC. This supports the ongoing investigation of PAL+ET in early breast cancer (NCT02513394).

Table. Pooled hematologic AEs: all grades and all causality clustered PTs reported for ≥10% of PAL+ET (LET/FUL)-treated ptsTime interval, mo0–&lt;66–&lt;1212–&lt;1818–&lt;2424–&lt;3030–&lt;36≥36Patients, N8726764912891192711TEAEs, %       Neutropenia75.758.649.349.842.937.054.5Leukopenia40.027.416.711.87.611.118.2Anemia20.812.710.011.19.211.118.2Thrombocytopenia15.18.76.15.55.914.836.4TEAEs=treatment-emergent adverse events.

Sponsor: Pfizer.

Citation Format: Diéras V, Rugo HS, Gelmon K, Finn RS, Cristofanilli M, Loi S, Colleoni M, Lu D, Gauthier E, Huang-Bartlett C, Turner NC, Schnell P. Long-term safety of palbociclib in combination with endocrine therapy in treatment-naive and previously treated women with HR+ HER2– advanced breast cancer: A pooled analysis from randomized phase 2 and 3 studies [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-22-07.

High-Level Clonal FGFR Amplification and Response to FGFR Inhibition in a Translational Clinical Trial

FGFR1 and FGFR2 are amplified in many tumor types, yet what determines response to FGFR inhibition in amplified cancers is unknown. In a translational clinical trial, we show that gastric cancers with high-level clonal FGFR2 amplification have a high response rate to the selective FGFR inhibitor AZD4547, whereas cancers with subclonal or low-level amplification did not respond. Using cell lines and patient-derived xenograft models, we show that high-level FGFR2 amplification initiates a distinct oncogene addiction phenotype, characterized by FGFR2-mediated transactivation of alternative receptor kinases, bringing PI3K/mTOR signaling under FGFR control. Signaling in low-level FGFR1-amplified cancers is more restricted to MAPK signaling, limiting sensitivity to FGFR inhibition. Finally, we show that circulating tumor DNA screening can identify high-level clonally amplified cancers. Our data provide a mechanistic understanding of the distinct pattern of oncogene addiction seen in highly amplified cancers and demonstrate the importance of clonality in predicting response to targeted therapy.

SIGNIFICANCE

Robust single-agent response to FGFR inhibition is seen only in high-level FGFR-amplified cancers, with copy-number level dictating response to FGFR inhibition in vitro, in vivo, and in the clinic. High-level amplification of FGFR2 is relatively rare in gastric and breast cancers, and we show that screening for amplification in circulating tumor DNA may present a viable strategy to screen patients. Cancer Discov; 6(8); 838-51. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 803.

Abstract 2825: Identification of CDK4/6-response biomarkers using estrogen receptor-positive breast cancer patient-derived xenografts (PDX)

Endocrine resistance is a clinical challenge for the treatment of estrogen receptor positive (ER+) breast cancer (BC). CDK4/6 blockade in combination with endocrine therapy has shown clinical activity in metastatic ER+ BC refractory to anti-hormonal treatment. However, there is a need for biomarkers that can predict the response to this treatment and improve patient stratification. We aimed to address this issue using xenograft models established from samples of ER+ BC patients.

Six ER+ PDXs were treated with continuous doses of a CDK4/6 inhibitor (LEE011, 75mg/kg, 6IW) and a PI3K-alpha inhibitor (BYL719, 35mg/kg, 6IW) as single agents and in combination, and intrinsic sensitivity to these agents was evaluated. The models were then genomically characterized using a capture-based sequencing panel and by digital PCR.

One PDX model was intrinsically sensitive to single-agent CDK4/6 inhibition and experienced tumor regression, but all individual tumors eventually escaped therapy after 50 days of treatment. This particular model harbored an ESR1-mutation and concomitant losses of CDKN2A/B. At relapse, we identified the acquisition of an RB1 frameshift mutation. Interestingly, upfront combined treatment with a PI3K-alpha inhibitor delayed the onset of tumor progression. Two out of the remaining five CDK4/6-resistant PDXs harbored either a frameshift mutation in RB1 (plus loss of heterozygosity) or had low pRb protein expression. Two other resistant models harbored CCND1 and MYC amplifications. The remaining one harbored a TSC1 loss. In all the CDK4/6-resistant PDX, however, the combination of CDK4/6 and PI3K-alpha inhibition resulted in tumor regression.

From our results, we conclude that loss of G1-cell cycle checkpoint control, such as mutation/loss of RB1 and CCND1-amplification, is associated with lack of response to CDK4/6 blockade in ER+ BC PDX. The addition of a PI3K-alpha inhibitor results in improvement of disease control in all experimental models tested.

Citation Format: Violeta Serra, Marta Palafox, Maria-Teresa Herrera, Martin A Rivas, Marta Guzmán, Olga Rodriguez, Judit Grueso, Meritxell Bellet, Mafalda Oliveira, Cristina Saura, Emmanuelle di Tomaso, Giordi Camponigro, Nicholas C. Turner, Javier Cortés, José Baselga. Identification of CDK4/6-response biomarkers using estrogen receptor-positive breast cancer patient-derived xenografts (PDX). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2825.

Palbociclib in Combination With Fulvestrant in Women With Hormone Receptor-Positive/HER2-Negative Advanced Metastatic Breast Cancer: Detailed Safety Analysis From a Multicenter, Randomized, Placebo-Controlled, Phase III Study (PALOMA-3)

BACKGROUND

Palbociclib enhances endocrine therapy and improves clinical outcomes in hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (MBC). Because this is a new target, it is clinically important to understand palbociclib's safety profile to effectively manage toxicity and optimize clinical benefit.

MATERIALS AND METHODS

Patients with endocrine-resistant, HR-positive/HER2-negative MBC (n = 521) were randomly assigned 2:1 to receive fulvestrant (500 mg intramuscular injection) with or without goserelin with oral palbociclib (125 mg daily; 3 weeks on/1 week off) or placebo. Safety assessments at baseline and day 1 of each cycle included blood counts on day 15 for the first 2 cycles. Hematologic toxicity was assessed by using laboratory data.

RESULTS

A total of 517 patients were treated (palbociclib, n = 345; placebo, n = 172); median follow-up was 8.9 months. With palbociclib, neutropenia was the most common grade 3 (55%) and 4 (10%) adverse event; median times to onset and duration of grade ≥3 episodes were 16 and 7 days, respectively. Asian ethnicity and below-median neutrophil counts at baseline were significantly associated with an increased chance of developing grade 3-4 neutropenia with palbociclib. Dose modifications for grade 3-4 neutropenia had no adverse effect on progression-free survival. In the palbociclib arm, febrile neutropenia occurred in 3 (<1%) patients. The percentage of grade 1-2 infections was higher than in the placebo arm. Grade 1 stomatitis occurred in 8% of patients.

CONCLUSION

Palbociclib plus fulvestrant treatment was well-tolerated, and the primary toxicity of asymptomatic neutropenia was effectively managed by dose modification without apparent loss of efficacy. This study appears at ClinicalTrials.gov, NCT01942135.

IMPLICATIONS FOR PRACTICE

Treatment with palbociclib in combination with fulvestrant was generally safe and well-tolerated in patients with hormone receptor (HR)-positive metastatic breast cancer. Consistent with the drug's proposed mechanism of action, palbociclib-related neutropenia differs in its clinical time course, patterns, and consequences from those seen with chemotherapy. Neutropenia can be effectively managed by a dose reduction, interruption, or cycle delay without compromising efficacy. A significant efficacy gain and a favorable safety profile support the consideration of incorporating palbociclib into the routine management of HR-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer.

Plasma ESR1 Mutations and the Treatment of Estrogen Receptor-Positive Advanced Breast Cancer

PURPOSE

ESR1 mutations are selected by prior aromatase inhibitor (AI) therapy in advanced breast cancer. We assessed the impact of ESR1 mutations on sensitivity to standard therapies in two phase III randomized trials that represent the development of the current standard therapy for estrogen receptor-positive advanced breast cancer.

MATERIALS AND METHODS

In a prospective-retrospective analysis, we assessed ESR1 mutations in available archived baseline plasma from the SoFEA (Study of Faslodex Versus Exemestane With or Without Arimidex) trial, which compared exemestane with fulvestrant-containing regimens in patients with prior sensitivity to nonsteroidal AI and in baseline plasma from the PALOMA3 (Palbociclib Combined With Fulvestrant in Hormone Receptor-Positive HER2-Negative Metastatic Breast Cancer After Endocrine Failure) trial, which compared fulvestrant plus placebo with fulvestrant plus palbociclib in patients with progression after receiving prior endocrine therapy. ESR1 mutations were analyzed by multiplex digital polymerase chain reaction.

RESULTS

In SoFEA, ESR1 mutations were found in 39.1% of patients (63 of 161), of whom 49.1% (27 of 55) were polyclonal, with rates of mutation detection unaffected by delays in processing of archival plasma. Patients with ESR1 mutations had improved progression-free survival (PFS) after taking fulvestrant (n = 45) compared with exemestane (n = 18; hazard ratio [HR], 0.52; 95% CI, 0.30 to 0.92; P = .02), whereas patients with wild-type ESR1 had similar PFS after receiving either treatment (HR, 1.07; 95% CI, 0.68 to 1.67; P = .77). In PALOMA3, ESR1 mutations were found in the plasma of 25.3% of patients (91 of 360), of whom 28.6% (26 of 91) were polyclonal, with mutations associated with acquired resistance to prior AI. Fulvestrant plus palbociclib improved PFS compared with fulvestrant plus placebo in both ESR1 mutant (HR, 0.43; 95% CI, 0.25 to 0.74; P = .002) and ESR1 wild-type patients (HR, 0.49; 95% CI, 0.35 to 0.70; P < .001).

CONCLUSION

ESR1 mutation analysis in plasma after progression after prior AI therapy may help direct choice of further endocrine-based therapy. Additional confirmatory studies are required.

Treating cancer with selective CDK4/6 inhibitors

Uncontrolled cellular proliferation, mediated by dysregulation of the cell-cycle machinery and activation of cyclin-dependent kinases (CDKs) to promote cell-cycle progression, lies at the heart of cancer as a pathological process. Clinical implementation of first-generation, nonselective CDK inhibitors, designed to inhibit this proliferation, was originally hampered by the high risk of toxicity and lack of efficacy noted with these agents. The emergence of a new generation of selective CDK4/6 inhibitors, including ribociclib, abemaciclib and palbociclib, has enabled tumour types in which CDK4/6 has a pivotal role in the G1-to-S-phase cell-cycle transition to be targeted with improved effectiveness, and fewer adverse effects. Results of pivotal phase III trials investigating palbociclib in patients with advanced-stage oestrogen receptor (ER)-positive breast cancer have demonstrated a substantial improvement in progression-free survival, with a well-tolerated toxicity profile. Mechanisms of acquired resistance to CDK4/6 inhibitors are beginning to emerge that, although unwelcome, might enable rational post-CDK4/6 inhibitor therapeutic strategies to be identified. Extending the use of CDK4/6 inhibitors beyond ER-positive breast cancer is challenging, and will likely require biomarkers that are predictive of a response, and the use of combination therapies in order to optimize CDK4/6 targeting.

Early Adaptation and Acquired Resistance to CDK4/6 Inhibition in Estrogen Receptor-Positive Breast Cancer

Small-molecule inhibitors of the CDK4/6 cell-cycle kinases have shown clinical efficacy in estrogen receptor (ER)-positive metastatic breast cancer, although their cytostatic effects are limited by primary and acquired resistance. Here we report that ER-positive breast cancer cells can adapt quickly to CDK4/6 inhibition and evade cytostasis, in part, via noncanonical cyclin D1-CDK2-mediated S-phase entry. This adaptation was prevented by cotreatment with hormone therapies or PI3K inhibitors, which reduced the levels of cyclin D1 (CCND1) and other G1-S cyclins, abolished pRb phosphorylation, and inhibited activation of S-phase transcriptional programs. Combined targeting of both CDK4/6 and PI3K triggered cancer cell apoptosis in vitro and in patient-derived tumor xenograft (PDX) models, resulting in tumor regression and improved disease control. Furthermore, a triple combination of endocrine therapy, CDK4/6, and PI3K inhibition was more effective than paired combinations, provoking rapid tumor regressions in a PDX model. Mechanistic investigations showed that acquired resistance to CDK4/6 inhibition resulted from bypass of cyclin D1-CDK4/6 dependency through selection of CCNE1 amplification or RB1 loss. Notably, although PI3K inhibitors could prevent resistance to CDK4/6 inhibitors, they failed to resensitize cells once resistance had been acquired. However, we found that cells acquiring resistance to CDK4/6 inhibitors due to CCNE1 amplification could be resensitized by targeting CDK2. Overall, our results illustrate convergent mechanisms of early adaptation and acquired resistance to CDK4/6 inhibitors that enable alternate means of S-phase entry, highlighting strategies to prevent the acquisition of therapeutic resistance to these agents. Cancer Res; 76(8); 2301-13. ©2016 AACR.

Fulvestrant plus palbociclib versus fulvestrant plus placebo for treatment of hormone-receptor-positive, HER2-negative metastatic breast cancer that progressed on previous endocrine therapy (PALOMA-3): final analysis of the multicentre, double-blind, phase 3 randomised controlled trial

BACKGROUND

In the PALOMA-3 study, the combination of the CDK4 and CDK6 inhibitor palbociclib and fulvestrant was associated with significant improvements in progression-free survival compared with fulvestrant plus placebo in patients with metastatic breast cancer. Identification of patients most suitable for the addition of palbociclib to endocrine therapy after tumour recurrence is crucial for treatment optimisation in metastatic breast cancer. We aimed to confirm our earlier findings with this extended follow-up and show our results for subgroup and biomarker analyses.

METHODS

In this multicentre, double-blind, randomised phase 3 study, women aged 18 years or older with hormone-receptor-positive, HER2-negative metastatic breast cancer that had progressed on previous endocrine therapy were stratified by sensitivity to previous hormonal therapy, menopausal status, and presence of visceral metastasis at 144 centres in 17 countries. Eligible patients-ie, any menopausal status, Eastern Cooperative Oncology Group performance status 0-1, measurable disease or bone disease only, and disease relapse or progression after previous endocrine therapy for advanced disease during treatment or within 12 months of completion of adjuvant therapy-were randomly assigned (2:1) via a centralised interactive web-based and voice-based randomisation system to receive oral palbociclib (125 mg daily for 3 weeks followed by a week off over 28-day cycles) plus 500 mg fulvestrant (intramuscular injection on days 1 and 15 of cycle 1; then on day 1 of subsequent 28-day cycles) or placebo plus fulvestrant. The primary endpoint was investigator-assessed progression-free survival. Analysis was by intention to treat. We also assessed endocrine therapy resistance by clinical parameters, quantitative hormone-receptor expression, and tumour PIK3CA mutational status in circulating DNA at baseline. This study is registered with ClinicalTrials.gov, NCT01942135.

FINDINGS

Between Oct 7, 2013, and Aug 26, 2014, 521 patients were randomly assigned, 347 to fulvestrant plus palbociclib and 174 to fulvestrant plus placebo. Study enrolment is closed and overall survival follow-up is in progress. By March 16, 2015, 259 progression-free-survival events had occurred (145 in the fulvestrant plus palbociclib group and 114 in the fulvestrant plus placebo group); median follow-up was 8·9 months (IQR 8·7-9·2). Median progression-free survival was 9·5 months (95% CI 9·2-11·0) in the fulvestrant plus palbociclib group and 4·6 months (3·5-5·6) in the fulvestrant plus placebo group (hazard ratio 0·46, 95% CI 0·36-0·59, p<0·0001). Grade 3 or 4 adverse events occurred in 251 (73%) of 345 patients in the fulvestrant plus palbociclib group and 38 (22%) of 172 patients in the fulvestrant plus placebo group. The most common grade 3 or 4 adverse events were neutropenia (223 [65%] in the fulvestrant plus palbociclib group and one [1%] in the fulvestrant plus placebo group), anaemia (ten [3%] and three [2%]), and leucopenia (95 [28%] and two [1%]). Serious adverse events (all causalities) occurred in 44 patients (13%) of 345 in the fulvestrant plus palbociclib group and 30 (17%) of 172 patients in the fulvestrant plus placebo group. PIK3CA mutation was detected in the plasma DNA of 129 (33%) of 395 patients for whom these data were available. Neither PIK3CA status nor hormone-receptor expression level significantly affected treatment response.

INTERPRETATION

Fulvestrant plus palbociclib was associated with significant and consistent improvement in progression-free survival compared with fulvestrant plus placebo, irrespective of the degree of endocrine resistance, hormone-receptor expression level, and PIK3CA mutational status. The combination could be considered as a therapeutic option for patients with recurrent hormone-receptor-positive, HER2-negative metastatic breast cancer that has progressed on previous endocrine therapy.

FUNDING

Pfizer.

Abstract P4-13-03: Updated safety from a double-blind phase 3 trial (PALOMA-3) of fulvestrant with placebo or with palbociclib in pre- and postmenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer that progressed on prior endocrine therapy

Background: Endocrine therapy (ET) resistance remains a major clinical problem for patients (pts) with hormone receptor (HR+) breast cancer (BC). In PALOMA-3, palbociclib (P) combined with fulvestrant (F) demonstrated significant prolongation of progression-free survival (PFS) vs F plus placebo (PLB) in pre/peri and postmenopausal women with HR+/HER2– metastatic BC (MBC) whose disease progressed on prior ET (median PFS 9.2 vs 3.8 m; HR=0.422, P=0.0001).

Methods: In this double-blind phase 3 study, 521 pts with HR+/HER2– MBC were randomized 2:1 to receive P (125 mg/d orally for 3 weeks followed by 1 week off) and F (500 mg given per standard of care) or PLB plus F. Pre- and perimenopausal women also received goserelin. One previous line of chemotherapy (CT) for MBC was allowed. Safety assessments occurred at baseline and D1 of each cycle; blood counts occurred every 2 wks for the first 2 cycles and on D1 of subsequent cycles. As pts may have experienced multiple episodes of neutropenia during treatment, we analyzed all episodes in aggregate based on laboratory data per CTCAE4.0.

Results: The results reported here are from the data cutoff of Dec 2014, with a median follow-up of 5.6 m. Overall rate of any grade (G) and G3/4 AEs was 98/70% of pts in P+F vs 89/18% in PLB+F. The most commonly reported AEs in P+F (≥20%) were hematologic toxicities, fatigue, nausea, and headache. Per lab data, G3/G4 neutropenia occurred in 52.2/8.2%, G3/G4 leukopenia in 39.5/1.2%, G3/G4 anemia in 20.8/2.9% and G3/G4 thrombocytopenia in 2.1/1.2% of pts on P+F. Neutropenia occurred early, with a median onset time for first episode of ≥G3 neutropenia of 15 d (13–197) and median time from first dose to the lowest absolute neutrophil count (ANC) of 29 d (13–334). The median duration of ≥G3 episode was 7 d (1–35), suggesting that most pts can resume treatment after a 1-week cycle delay. A comparable proportion of any grade neutropenia was observed in pts with or without prior CT (prior CT 88.4% vs no prior CT 85.4%). There was no difference in the rate of G3/G4 neutropenia in the older pts (&gt;65 yrs, 51% vs ≤65 yrs, 57%) in P+F arm. Concurrent G≥3 infections occurred in 1% of pts with G≥3 neutropenia (2/192 pts). Febrile neutropenia occurred in 0.6% of pts in both arms. 21% of pts had dose reductions and 45% had dose interruption due to neutropenia. Dose intensity was maintained at 89.7% for P. Serious adverse events (SAEs) were reported in 9.6% of pts on P+F and in 14% of pts on PLB+F. The most common SAEs on P+F were pulmonary embolism (0.9%) and pyrexia (0.9%). Safety analyses with longer follow-up (data cut off, March 2015) are ongoing and will be presented.

Conclusions: Findings suggest P+F has a favorable safety profile characterized mainly by asymptomatic hematologic toxicity. Overall SAE rates were low and comparable between the 2 arms. Palbociclib-related neutropenia differs from that seen with CT, consistent with proposed mechanism of action, in that it is not commonly associated with fever, and can be effectively managed by a dose interruption or cycle delay.

Funding: Pfizer, Inc.

Citation Format: Verma S, DeMichele AM, Loi S, Ro J, Colleoni M, Iwata H, Harbeck N, Stearns V, Cristofanilli M, Huang Bartlett C, Schnell P, Zhang K, Thiele A, Turner NC, Rugo HS. Updated safety from a double-blind phase 3 trial (PALOMA-3) of fulvestrant with placebo or with palbociclib in pre- and postmenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer that progressed on prior endocrine therapy. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-13-03.

Abstract OT1-03-17: ABRAZO: An international phase 2 (2-stage, 2-cohort) study of the oral PARP inhibitor talazoparib (BMN 673) in BRCA mutation subjects with locally advanced and/or metastatic breast cancer

Background: Cancer cells with deleterious mutations in breast cancer susceptibility genes 1 and 2 (BRCA1/2) are deficient in the DNA double-strand break repair mechanism, rendering them highly dependent on the single-strand break repair pathway, which is initiated by poly-(ADP-ribose) polymerase (PARP) [1-3]. In cells with deleterious BRCA1/2 mutations, PARP inhibition is synthetically lethal because of accumulation of irreparable DNA damage [1-3]. Talazoparib (BMN 673) exhibits a novel two-pronged approach in treating BRCA1/2-mutant tumors: 1) potent catalytic inhibition of the PARP enzyme; and 2) trapping of PARP at sites of DNA damage [4-7]. The capacity to trap PARP-DNA complexes varies widely across PARP inhibitors and is not correlated with catalytic inhibition potency [4-7]. In preclinical models, trapping PARP on DNA is more potent at inducing cancer cell death than enzymatic inhibition of PARP alone [4,7]. Talazoparib is the most potent clinical-stage PARP inhibitor tested to date with the highest efficacy at trapping PARP-DNA complexes [7]. Talazoparib has shown single-agent antitumor efficacy in several solid tumor types and was generally well tolerated in a phase 1/2 clinical study [8].

Methods: This 2-stage, 2-cohort, phase 2 international study (ABRAZO) evaluates the safety and efficacy of talazoparib in patients with a deleterious germline BRCA1 or BRCA2 mutation with locally advanced and/or metastatic breast cancer. Eligible subjects will be assigned to one of two cohorts based on prior chemotherapy for metastatic disease. Cohort 1 (n=70) includes patients with a complete response (CR) or partial response (PR) to platinum-containing regimens for metastatic disease. Cohort 2 (n=70) includes patients who have received &gt;2 prior chemotherapy regimens in the metastatic setting but have not had prior platinum therapy for locally advanced or metastatic disease (prior adjuvant or neoadjuvant therapy with a platinum is allowed). The primary objective is objective response rate (ORR). Secondary objectives include clinical benefit response (CBR) rate, duration of response (DOR), progression-free survival (PFS), and overall survival (OS). Health-related quality of life (QoL) assessments are an exploratory objective. Eligible subjects will receive oral talazoparib (1 mg/day, 21-day cycles) until disease progression or unacceptable toxicity. This trial is currently enrolling patients from the United States and Europe (NCT02034916).

This study is funded by BioMarin Pharmaceutical Inc.

References:

1. Ashworth A. J Clin Oncol. 2008;26:3785-3790; 2. Jalve M, Curtin NJ. Ther Adv Med Oncol. 2011;3:257-267; 3. Helleday T. Mol Oncol. 2011;5:387-393; 4. Murai J et al. Cancer Res. 2012;72:5588-5599; 5. Rouleau M et al. Nat Rev Cancer. 2010;10:293-301; 6. Shen Y et al. Clin Cancer Res. 2013;19:5003-5015; 7. Murai J et al. Mol Cancer Ther. 2014;13:433-443; 8. Wainberg ZA et al. J Clin Oncol. 2014;32(suppl):5. Abstract 7522.

Citation Format: Turner NC, Balmaña J, Fasching PA, Hurvitz SA, Rugo HS, Telli ML, Visco F, Wardley AM, Yang X, Lokker NA, Lounsbury DL, Robson ME. ABRAZO: An international phase 2 (2-stage, 2-cohort) study of the oral PARP inhibitor talazoparib (BMN 673) in BRCA mutation subjects with locally advanced and/or metastatic breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr OT1-03-17.

Abstract P4-13-01: PALOMA3: Phase 3 trial of fulvestrant with or without palbociclib in pre- and postmenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer that progressed on prior endocrine therapy—confirmed efficacy and safety

Background: Selective estrogen receptor modulators and aromatase inhibitors (AI) (+LHRH agonists [premenopausal]) are standard of care (SOC) for hormone–receptor–positive (HR+) metastatic breast cancer (MBC). Many HR+ MBC patients (pts) get limited benefit from adjuvant or advanced endocrine therapy (ET) and develop endocrine resistance, refractory disease. HR+ BC growth relies on cyclin dependent kinases 4/6 that promote G1–S phase cell cycle progression. Palbociclib (PAL) with ET showed efficacy in HR+/HER2– MBC (Turner et al, 2015). We report updated safety and efficacy from PALOMA3 with longer follow–up, focusing on degrees of clinically defined endocrine resistance.

Methods: Pts with HR+/HER2– MBC that progressed on prior ET were randomized 2:1 to PAL (125 mg/d oral [3 wks drug, 1 wk off]) + fulvestrant (F, 500 mg, SOC) +/– goserelin or placebo (PLB)+F. One line of chemotherapy (CT) for MBC was allowed. Pt stratification: prior ET sensitivity; visceral metastases; menopausal status. Primary endpoint (EP) was investigator–assessed progression–free survival (PFS). Secondary EP: overall survival, response assessment, patient–reported outcomes, safety.

Results: By March 2015, median follow–up was 8.9 mo. 521 pts were randomized (PAL+F, 347; PLB+F, 174). Baseline characteristics were balanced. Median PFS was 9.5 (95% CI 9.2–11.0) mo (PAL+F) vs 4.6 (3.5–5.6) mo (PLB+F) (HR 0.46 [0.36–0.59], P&lt;0.001). Overall response (CR+ PR) was significantly improved with PAL+F (ITT: 19% vs 8.6%, P=0.001; pts with measurable disease: 24.6% vs 10.9%, P&lt;0.001). Clinical benefit (CBR=CR+PR+SD ?24wks) was 66.6% vs 39.7% (P&lt;0.001). Benefit from PAL was confirmed in pre– and postmenopausal pts with PFS in premenopausal 9.5 vs 5.6 mo (HR=0.50 [0.29–0.87], P=0.006) and in postmenopausal 9.9 vs 3.9 mo (HR=0.45 [0.34–0.59], P&lt;0.001). Common adverse events (AEs) for PAL+F vs PLB+F were neutropenia (80.9 vs 3.5%), leukopenia (49.6 vs 4.1%), and fatigue (39.1 vs 28.5%); febrile neutropenia occurred in 0.9% (P+ F) vs 0.6% pts (PLB+F). Discontinuation due to AEs was 4.0% on P vs 1.7% on PLB. The benefit of PAL+F vs PLB+F was compared in pts with various degrees of endocrine resistance: a) progression ≤12 mo of adjuvant ET completion, PFS 9.5 vs 5.4 mo (HR 0.55 [0.32–0.92], P=0.01); b) failed 1 line of ET, 10.2 vs 5.4 mo (HR 0.42 [0.29–0.59], P&lt;0.001); c) failed 2 lines of ET, 9.9 vs 1.8 mo (HR=0.20 [0.10– 0.39, P&lt;0.001); d) proven endocrine sensitive, 10.2 vs 4.2 mo (HR 0.42 [0.32–0.56], P&lt;0.001); e) proven no prior endocrine sensitivity, 7.5 vs 5.4 mo (HR 0.64 [0.39–1.07], P=0.04) f) AI most recent therapy, 9.5 vs 3.7 mo (HR 0.42 [0.31–0.56], P&lt;0.001).

Conclusion: Mature efficacy confirmed superior PFS and demonstrated significantly improved clinical response and CBR by the combination of ET and Palbociclib. It also consistently showed therapeutic benefit irrespective of menopausal status and various degrees of endocrine sensitivity. Safety profile is favorable. PAL+F may be an effective option for HR+ MBC pts.

Funding: Pfizer.

Citation Format: Cristofanilli M, Bondarenko I, Ro J, Im S-A, Masuda N, Colleoni M, DeMichele AM, Loi S, Verma S, Iwata H, Huang Bartlett C, Zhang K, Puyana Theall K, Turner NC, Slamon DJ. PALOMA3: Phase 3 trial of fulvestrant with or without palbociclib in pre- and postmenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer that progressed on prior endocrine therapy—confirmed efficacy and safety. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-13-01.

Phase II study of AZD4547 in FGFR amplified tumours: Gastroesophageal cancer (GC) cohort pharmacodynamic and biomarker results

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Background: FGFR amplified tumors demonstrate oncogene addiction in vitro and in vivo. We examined the efficacy of AZD4547, an orally available inhibitor of FGFR 1, 2 & 3, in FGFR1/2 amplified cancers, and herein present results from a gastroesophageal cancer (GC) cohort. Methods: Phase II Simon 2 stage design (3 independent cohorts) for previously treated patients (pts) with advanced FGFR1 (HER2 negative breast/NSCLC) or FGFR2 amplified tumors. FGFR1/2 amplification was centrally assessed using FISH. Pts received AZD4547 80mg twice daily. Primary endpoint is centrally confirmed response rate (RR), with the study concluding efficacy if ≥ 3/17 patients in a cohort had a confirmed response. PET-CT was performed at baseline, D14 and 8 wks, biopsy at baseline and D14 and optionally on progression. Biomarkers included FGFR copy number variation in tumor and plasma, NanoString gene expression, MIRAX digital FISH imaging and phospho-immunohistochemistry. Results: Of 288 pts with screening results, 9% (12/138) gastroesophageal (GC) pts had FGFR2 amplification with 5% (7/138) highly amplified (FGFR2 ratio > 5.0). Confirmed RR was 33% (3/9) in FGFR2 amplified GC. Mean duration of response in responders was 5.7 months. All GC responders had a PET response on D14 PET. Common toxicities (all pts n = 18) included fatigue (72%), constipation (50%) mucositis, skin and eye changes (44% each). Phospho-immunohistochemistry on pre-treatment and D14 biopsies demonstrated an increase in S6 and decrease in p-ERK following treatment. Using digital droplet PCR (ddPCR) elevated FGFR2 copy number was detected in free plasma DNA of all responding GC pts, and no non-responding pt. NanoString and MIRAX imaging analysis revealed the presence of truncated C3 FGFR2 isoform and high level homogenous FGFR2 amplification in all GC responders respectively. Conclusions: AZD4547 demonstrated promising activity in FGFR2 amplified GC. On treatment biopsies demonstrate evidence of target inhibition. Clonal, high level amplification appears to be required for response to AZD4547. As all responding patients had FGFR2 copy number gain detected in plasma using ddPCR this technique will be developed as a screening tool. Clinical trial information: NCT01795768.

Abstract C37: Molecular determinants of sensitivity and resistance to FGFR inhibition in FGFR2-amplified gastric cancer

Despite improvements in diagnostics and chemotherapy regiments in gastric cancer, there is still an urgent need for novel biomarkers and second-line treatment interventions. High level FGFR2 amplification is found in ∼5% gastric cancers, and responses in FGFR2-amplified gastric cancer have been observed in a phase II study of FGFR inhibitor AZD4547 (Smyth et al ASCO 2015, NCT01795768). Here we studied tumor progression biopsies and patient-derived xenografts (PDX) to understand the mechanisms of sensitivity and resistance in FGFR2-amplified gastric cancer.

PDX models were generated from the baseline biopsies of two Caucasian patients with junctional FGFR2-amplified tumors who had durable responses to AZD4547 in the clinic. Both PDX recapitulated the histology of the original cancers, and whole exome sequencing demonstrated 85-90% agreement mutations between the patient biopsies and the PDX tumors. Similar to the patients, both models were highly sensitive to AZD4547, with regression of ∼60% seen after 10 days treatment, with subsequent stability on chronic dosing.

To understand the molecular mechanisms of sensitivity to AZD4547, we profiled PDX tumors and PDX-derived spheroid cultures with phospho-RTK signaling arrays and by western blot. Although FGFR inhibition resulted in short-term suppression of PI3K-mTOR signaling, chronic exposure resulted in an increase in phospho-S6 and phospho-4EBP1 after 24 hours of treatment. Combination of AZD4547 and the catalytic mTOR inhibitor AZD2014 elicited a greater response in vitro than either drug alone. To examine adaptive response to AZD4547 we excised residual PDX tumors after 60 days treatment, demonstrating upregulated ERBB3 and insulin receptor phosphorylation in tumors adapted to long-term FGFR inhibition. A treatment break, which resumed tumor growth, re-sensitized to AZD4547, suggesting that ongoing FGFR inhibition was required to maintain the adaptive response.

Finally we examined the mechanism of acquired resistance to AZD4547. Two responding patients had progression biopsies. Paired exome sequencing demonstrated an acquired KRAS amplification in one patient, though no evident onco-mutation was identified in patient two. In parallel, long-term treatment of PDX with AZD4547 gave rise to resistant PDX tumors, the results of which will be presented at the conference.

In conclusion, we show that reactivation of mTOR signaling limits sensitivity of FGFR2-amplified tumors to AZD4547, identifying potential combination strategies to deepen response. Studies of acquired resistance are ongoing, with preliminary evidence suggesting acquisition of downstream genetic events.

Citation Format: Irina Babina, Alex Pearson, Ros Cutts, Elizabeth Smyth, Jian Ning, Amanda Swain, David Cunningham, Nicholas C. Turner. Molecular determinants of sensitivity and resistance to FGFR inhibition in FGFR2-amplified gastric cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C37.

Analysis of ESR1 mutation in circulating tumor DNA demonstrates evolution during therapy for metastatic breast cancer

Acquired ESR1 mutations are a major mechanism of resistance to aromatase inhibitors (AIs). We developed ultra high-sensitivity multiplex digital polymerase chain reaction assays for ESR1 mutations in circulating tumor DNA (ctDNA) and investigated the clinical relevance and origin of ESR1 mutations in 171 women with advanced breast cancer. ESR1 mutation status in ctDNA showed high concordance with contemporaneous tumor biopsies and was accurately assessed in samples shipped at room temperature in preservative tubes. ESR1 mutations were found exclusively in estrogen receptor-positive breast cancer patients previously exposed to AI. Patients with ESR1 mutations had a substantially shorter progression-free survival on subsequent AI-based therapy [hazard ratio, 3.1; 95% confidence interval (CI), 1.9 to 23.1; P = 0.0041]. ESR1 mutation prevalence differed markedly between patients who were first exposed to AI during the adjuvant and metastatic settings [5.8% (3 of 52) versus 36.4% (16 of 44), respectively; P = 0.0002]. In an independent cohort, ESR1 mutations were identified in 0% (0 of 32; 95% CI, 0 to 10.9) tumor biopsies taken after progression on adjuvant AI. In a patient with serial sampling, ESR1 mutation was selected during metastatic AI therapy to become the dominant clone in the cancer. ESR1 mutations can be robustly identified with ctDNA analysis and predict for resistance to subsequent AI therapy. ESR1 mutations are rarely acquired during adjuvant AI but are commonly selected by therapy for metastatic disease, providing evidence that mechanisms of resistance to targeted therapy may be substantially different between the treatment of micrometastatic and overt metastatic cancer.

Efficient Genotyping of KRAS Mutant Non-Small Cell Lung Cancer Using a Multiplexed Droplet Digital PCR Approach

Droplet digital PCR (ddPCR) can be used to detect low frequency mutations in oncogene-driven lung cancer. The range of KRAS point mutations observed in NSCLC necessitates a multiplex approach to efficient mutation detection in circulating DNA. Here we report the design and optimisation of three discriminatory ddPCR multiplex assays investigating nine different KRAS mutations using PrimePCR™ ddPCR™ Mutation Assays and the Bio-Rad QX100 system. Together these mutations account for 95% of the nucleotide changes found in KRAS in human cancer. Multiplex reactions were optimised on genomic DNA extracted from KRAS mutant cell lines and tested on DNA extracted from fixed tumour tissue from a cohort of lung cancer patients without prior knowledge of the specific KRAS genotype. The multiplex ddPCR assays had a limit of detection of better than 1 mutant KRAS molecule in 2,000 wild-type KRAS molecules, which compared favourably with a limit of detection of 1 in 50 for next generation sequencing and 1 in 10 for Sanger sequencing. Multiplex ddPCR assays thus provide a highly efficient methodology to identify KRAS mutations in lung adenocarcinoma.

Mutation tracking in circulating tumor DNA predicts relapse in early breast cancer

The identification of early-stage breast cancer patients at high risk of relapse would allow tailoring of adjuvant therapy approaches. We assessed whether analysis of circulating tumor DNA (ctDNA) in plasma can be used to monitor for minimal residual disease (MRD) in breast cancer. In a prospective cohort of 55 early breast cancer patients receiving neoadjuvant chemotherapy, detection of ctDNA in plasma after completion of apparently curative treatment-either at a single postsurgical time point or with serial follow-up plasma samples-predicted metastatic relapse with high accuracy [hazard ratio, 25.1 (confidence interval, 4.08 to 130.5; log-rank P < 0.0001) or 12.0 (confidence interval, 3.36 to 43.07; log-rank P < 0.0001), respectively]. Mutation tracking in serial samples increased sensitivity for the prediction of relapse, with a median lead time of 7.9 months over clinical relapse. We further demonstrated that targeted capture sequencing analysis of ctDNA could define the genetic events of MRD, and that MRD sequencing predicted the genetic events of the subsequent metastatic relapse more accurately than sequencing of the primary cancer. Mutation tracking can therefore identify early breast cancer patients at high risk of relapse. Subsequent adjuvant therapeutic interventions could be tailored to the genetic events present in the MRD, a therapeutic approach that could in part combat the challenge posed by intratumor genetic heterogeneity.

Abstract CT331: “BEECH”, a phase I/II study of the AKT inhibitor AZD5363 combined with paclitaxel in patients with advanced or metastatic breast cancer: results from the dose-finding study, including quantitative assessment of circulating tumor DNA as a s

Background: The PI3K/AKT/MTOR pathway is frequently de-regulated in breast cancer. AZD5363 (AZD) is a potent selective inhibitor of AKT1-3. We report the dose-finding phase assessing the safety/tolerability of two intermittent weekly dosing schedules of AZD combined with paclitaxel (P) in HER2 negative breast cancer. The study incorporates prospective assessment of whether circulating tumour DNA (ctDNA) analysis can predict response/resistance earlier than conventional RECIST.

Design: AZD capsules were dosed p.o. in one of two schedules: “4/3” (4 days on-treatment followed by 3 days off, starting 360 mg twice daily (bd)) or “2/5” (2 days on-5 days off, starting 560 mg bd). Both schedules comprised 3 weeks P 90 mg/m2 IV on Day 1 with AZD started on Day 2, and 1 week off-treatment. Patients who stopped P were able to continue AZD alone at investigators’ discretion. Escalating doses of AZD were evaluated in cohorts of 3-6 evaluable patients treated until disease progression, unacceptable toxicity, or withdrawal of consent. A safety review committee reviewed safety data and dose limiting toxicities (DLTs) prior to dose modification. Plasma samples for ctDNA extraction were collected at baseline, weekly in cycle 1, day 1 of all subsequent cycles, and were analysed by digital PCR. Female patients aged ≥18 years with HER2 negative MBC and up to two prior chemotherapy courses for advanced cancer were recruited.

Results: 37 patients have received AZD. DLTs in 2/6 patients at 480 mg 4/3 comprised one patient with maculo-papular rash, and another with immune allergic reaction (both CTCAE grade 3). No DLT was observed in the 400 mg 4/3 cohort, which was defined as the maximum tolerated dose (MTD) in combination with P. DLTs in 2/6 patients at 640 mg 2/5 comprised one patient with prolonged neutropaenia (grade 4), and another with diarrhoea (grade 3). No DLTs were observed in 11 patients on the 560 mg 2/5 cohort. In all patients median progression free survival was 8.2 months, despite pre-treatment with taxane chemotherapy in 62% patients and a median of 2 prior lines of chemotherapy. A patient with Cowden's syndrome (PTEN germline mutation) had a partial response maintained for 18 months, including 12 months on AZD5363 alone. ctDNA assessment suggests that lack of a fall in ctDNA abundance may predict for early progression.

Conclusions: AZD5363 400mg bd 4/3 in combination with paclitaxel was determined to be well tolerated in patients with MBC, with investigation of the 2/5 schedule continuing. Two international double-blind randomised studies have commenced to assess AZD5363 400 mg bd 4/3 schedule combined with paclitaxel versus paclitaxel plus placebo in ER positive HER2 negative MBC stratified by PIK3CA mutation status (BEECH Part B), and in triple negative breast cancer (PAKT).

Citation Format: Nicholas C. Turner, Mafalda Oliveira, Anne Armstrong, Marie-Paule Sablin, José A. Perez-Fidalgo, Sarah Herebien, Isaac Garcia-Murillas, Stan Johnson, Andrew Foxley, Adnan Mahmood, Justin P. Lindemann. “BEECH”, a phase I/II study of the AKT inhibitor AZD5363 combined with paclitaxel in patients with advanced or metastatic breast cancer: results from the dose-finding study, including quantitative assessment of circulating tumor DNA as a s [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr CT331. doi:10.1158/1538-7445.AM2015-CT331