An Open-label Phase I Study of GDC-0927 in Postmenopausal Women with Locally Advanced or Metastatic Estrogen Receptor-Positive Breast Cancer

PURPOSE

GDC-0927 is a novel, potent, nonsteroidal, orally bioavailable, selective estrogen receptor (ER) degrader that induces tumor regression in ER+ breast cancer xenograft models.

PATIENTS AND METHODS

This phase I dose-escalation multicenter study enrolled postmenopausal women with ER+/HER2- metastatic breast cancer to determine the safety, pharmacokinetics, and recommended phase II dose of GDC-0927. Pharmacodynamics was assessed with [18F]-fluoroestradiol (FES) PET scans.

RESULTS

Forty-two patients received GDC-0927 once daily. The MTD was not reached. The most common adverse events (AE) regardless of causality were nausea, constipation, diarrhea, arthralgia, fatigue, hot flush, back pain, and vomiting. There were no deaths, grade 4/5 AEs, or treatment-related serious AEs. Two patients experienced grade 2 AEs of special interest of deep vein thrombosis and jugular vein thrombosis, both considered unrelated to GDC-0927. Following dosing, approximately 1.6-fold accumulation was observed, consistent with the observed half-life and dosing frequency. There were no complete or partial responses. Pharmacodynamics was supported by >90% reduction in FES uptake and an approximately 40% reduction in ER expression, suggesting ER degradation is not the mechanistic driver of ER antagonism. Twelve patients (29%) achieved clinical benefit; 17 patients (41%) showed a confirmed best overall response of stable disease. Baseline levels of ER and progesterone receptor protein and mutant ESR1 circulating tumor DNA did not correlate with clinical benefit.

CONCLUSIONS

GDC-0927 appeared to be well tolerated with pharmacokinetics supporting once-daily dosing. There was evidence of target engagement and preliminary evidence of antitumor activity in heavily pretreated patients with advanced/metastatic ER+/HER2- breast cancer with and without ESR1 mutations.

Genome-wide association studies of survival in 1520 cancer patients treated with bevacizumab-containing regimens

Germline variants might predict cancer progression. Bevacizumab improves overall survival (OS) in patients with advanced cancers. No biomarkers are available to identify patients that benefit from bevacizumab. A meta-analysis of genome-wide association studies (GWAS) was conducted in 1,520 patients from Phase III trials (CALGB 80303, 40503, 80405 and ICON7), where bevacizumab was randomized to treatment without bevacizumab. We aimed to identify genes and single nucleotide polymorphisms (SNPs) associated with survival independently of bevacizumab treatment or through interaction with bevacizumab. A cause-specific Cox model was used to test the SNP-OS association in both arms combined (prognostic), and the effect of SNPs-bevacizumab interaction on OS (predictive) in each study. The SNP effects across studies were combined using inverse variance. Findings were tested for replication in advanced colorectal and ovarian cancer patients from The Cancer Genome Atlas (TGCA). In the GWAS meta-analysis, patients with rs680949 in PRUNE2 experienced shorter OS compared to patients without it (P = 1.02 × 10^-7 , hazard ratio [HR] = 1.57, 95% confidence interval [CI] 1.33-1.86), as well as in TCGA (P = .0219, HR = 1.58, 95% CI 1.07-2.35). In the GWAS meta-analysis, patients with rs16852804 in BARD1 experienced shorter OS compared to patients without it (P = 1.40 × 10^-5 , HR = 1.51, 95% CI 1.25-1.82) as well as in TCGA (P = 1.39 × 10^-4 , HR = 3.09, 95% CI 1.73-5.51). Patients with rs3795897 in AGAP1 experienced shorter OS in the bevacizumab arm compared to the nonbevacizumab arm (P = 1.43 × 10^-5 ). The largest GWAS meta-analysis of bevacizumab treated patients identified PRUNE2 and BARD1 (tumor suppressor genes) as prognostic genes of colorectal and ovarian cancer, respectively, and AGAP1 as a potentially predictive gene that interacts with bevacizumab with respect to patient survival.

Real-world survival outcomes of heavily pretreated patients with refractory HR+, HER2-metastatic breast cancer receiving single-agent chemotherapy-a comparison with MONARCH 1

PURPOSE

In MONARCH 1 (NCT02102490), single-agent abemaciclib demonstrated promising efficacy activity and tolerability in a population of heavily pretreated women with refractory HR+, HER2- metastatic breast cancer (MBC). To help interpret these results and put in clinical context, we compared overall survival (OS) and duration of therapy (DoT) between MONARCH 1 and a real-world single-agent chemotherapy cohort.

METHODS

The real-world chemotherapy cohort was created from a Flatiron Health electronic health records-derived database based on key eligibility criteria from MONARCH 1. The chemotherapies included in the cohort were single-agent capecitabine, gemcitabine, eribulin, or vinorelbine. Results were adjusted for baseline demographics and clinical differences using Mahalanobis distance matching (primary analysis) and entropy balancing (sensitivity analysis). OS and DoT were analyzed using the Kaplan-Meier method and Cox proportional hazards regression.

RESULTS

A real-world single-agent chemotherapy cohort (n = 281) with eligibility criteria similar to the MONARCH 1 population (n = 132) was identified. The MONARCH 1 (n = 108) cohort was matched to the real-world chemotherapy cohort (n = 108). Median OS was 22.3 months in the abemaciclib arm versus 13.6 months in the matched real-world chemotherapy cohort with an estimated hazard ratio (HR) of 0.54. The median DoT was 4.1 months in MONARCH 1 compared to 2.9 months in the real-world chemotherapy cohort with HR of 0.76.

CONCLUSIONS

This study demonstrates an approach to create a real-world chemotherapy cohort suitable to serve as a comparator for trial data. These exploratory results suggest a survival advantage and place the benefit of abemaciclib monotherapy in clinical context.

Impact of breast cancer chemotherapy on ovarian damage and recovery

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Background: As societal shifts have led to more women delaying childbearing, a diagnosis of breast cancer is increasingly more likely to occur prior to the completion of family building. Therefore, understanding impact of chemo on future fertility is of the utmost importance. This study evaluates the trends in AMH over time in women receiving different chemo regimens for breast cancer. Methods: This is an IRB approved prospective study of 164 women, < 45 years old with non-metastatic breast cancer who were enrolled at time of diagnosis. Patients received chemo and had prospective serum AMH measured at baseline,12, 18 & 24 mos post-chemo. Of those, 99/164 completed 2-yr follow up. Pts were divided according to their chemotherapy regimen: ddAC-T, CMF and other (e.g. TH). Results: Mean age in ddAC-T (n = 118), CMF (n = 22) and other (n = 23) chemo groups were 37.1±4.6, 41.1±3.2 and 37.6±4.3 yrs, respectively (p = 0.001). AMH sharply declined between baseline & 12 mos post-chemo in all groups (p = 0.005). There was no difference in rate of decline between the groups, after adjusting for age. Age was an important predictor of AMH. Older age at study entry was associated with lower AMH with a decrease of 9% per life year (p = 0.0005). AMH recovered from 12 to 18 mos post-chemo in all groups. 18 mos after chemo, AMH recovery was observed in 61%, 59% & 65% in ddAC-T, CMF & other groups, respectively. In the ddAC-T arm there was a 1.9 fold increase in AMH while there was a 1.4 and 3.3 fold increase in the CMF and other arms, respectively. At 2-yrs post-chemo, AMH recovery rate reached 67%, 69% & 77% in ddAC-T, CMF & other groups, respectively. However, 12% in ddAC-T and 23% in CMF had undetectable AMH. Baseline AMH was 1.59 fold higher in pts whose AMH increased compared to those whose AMH decreased between 12 & 18 mos (p = 0.035). AMH recovery was associated with higher baseline AMH. Age, BMI & chemo type did not correlate with AMH recovery and tamoxifen treatment did not impact AMH recovery. Conclusions: Our data show that anthracycline plus taxane, taxane-based and CMF chemo regimens compromise ovarian reserve in breast cancer patients in similar fashion. As surviving ovarian follicles resume production of AMH, most of ovarian reserve recovery occurs by 18 mos post-chemo with some minor recovery from 18-24 mos. Baseline AMH level is the most important predictor of AMH recovery. Hence in women undergoing gonadotoxic chemo, ovarian reserve should be assessed by AMH before and 12 months after treatment to determine extent of damage. The novel information provided in this study is valuable for counseling cancer pts about fertility preservation. Clinical trial information: NCT00823654 .

Increased chemotherapy-induced ovarian reserve loss in women with germline BRCA mutations due to oocyte deoxyribonucleic acid double strand break repair deficiency

OBJECTIVE

To assess whether woman who have BRCA mutations (WBM) experience more declines in ovarian reserve after chemotherapy treatment, as it induces oocyte death by deoxyribonucleic acid (DNA) damage, and BRCA mutations result in DNA damage repair deficiency.

DESIGN

Longitudinal cohort study.

SETTING

Academic centers.

PATIENT(S)

The 108 evaluable women with breast cancer were stratified into those never tested (negative family history; n = 35) and those negative (n = 59) or positive (n = 14) for a pathogenic BRCA mutation.

INTERVENTION(S)

Sera were longitudinally obtained before and 12-24 months after chemotherapy treatment, assayed for antimüllerian hormone (AMH), and adjusted for age at sample collection.

MAIN OUTCOME MEASURE(S)

Ovarian recovery, defined as the geometric mean of the after chemotherapy age-adjusted AMH levels compared with baseline levels.

RESULT(S)

Compared with the controls, the before chemotherapy treatment AMH levels were 24% and 34% lower in those negative or positive for BRCA mutations, consistent with accelerated ovarian aging in WBM. The WBM had a threefold difference in AMH recovery after chemotherapy treatment (1.6%), when compared with BRCA negative (3.7%) and untested/low risk controls (5.2%). Limiting the analysis to the most common regimen, doxorubicin and cyclophosphamide followed by paclitaxel, showed similar results. These findings were mechanistically confirmed in an in vitro mouse oocyte BRCA knockdown bioassay, which showed that BRCA deficiency results in increased oocyte susceptibility to doxorubicin.

CONCLUSION(S)

Women who have pathogenic BRCA mutations are more likely to lose ovarian reserve after chemotherapy treatment, suggesting an emphasis on fertility preservation. Furthermore, our findings generate the hypothesis that DNA repair deficiency is a shared mechanism between aging, infertility, and cancer.

CLINICAL TRIAL REGISTRATION NUMBER

NCT00823654.

Double PIK3CA mutations in cis increase oncogenicity and sensitivity to PI3Kα inhibitors

Activating mutations in PIK3CA are frequent in human breast cancer, and phosphoinositide 3-kinase alpha (PI3Kα) inhibitors have been approved for therapy. To characterize determinants of sensitivity to these agents, we analyzed PIK3CA-mutant cancer genomes and observed the presence of multiple PIK3CA mutations in 12 to 15% of breast cancers and other tumor types, most of which (95%) are double mutations. Double PIK3CA mutations are in cis on the same allele and result in increased PI3K activity, enhanced downstream signaling, increased cell proliferation, and tumor growth. The biochemical mechanisms of dual mutations include increased disruption of p110α binding to the inhibitory subunit p85α, which relieves its catalytic inhibition, and increased p110α membrane lipid binding. Double PIK3CA mutations predict increased sensitivity to PI3Kα inhibitors compared with single-hotspot mutations.

Abstract P3-03-01: Double PIK3CA mutations in cis drive oncogene addiction and enhance sensitivity to PI3K alpha inhibitors in breast cancer

Activating mutations in PIK3CA, the gene coding for the catalytic subunit (p110α) of phosphoinositide-3-kinase (PI3K), are the most frequent oncogenic alterations in estrogen receptor-positive (ER+) breast cancer and are also prevalent in other tumor types. PI3Kα inhibitors including alpelisib have recently been shown to be clinically active in ER+ PIK3CA mutant breast cancer. To characterize determinants of sensitivity to these agents, we undertook a comprehensive analysis of PIK3CA mutant cancer genomes and observed the presence of double PIK3CA mutations in 12-15% of breast cancer and other tumor types. These double PIK3CA mutations are clonal, located in cis on the same allele, and are composed of a single hotspot mutation combined with a recurrent second-site mutation. Double PIK3CA mutations in cis result in increased PI3K activity and downstream signaling together with enhanced cell proliferation and tumor growth compared to single hotspot mutations. The biochemical mechanisms underlying this increased oncogenicity include increased disruption of p110α binding to the inhibitory subunit p85α, which relieves its catalytic inhibition, and increased membrane lipid binding. Finally, these double PIK3CA mutations predict for increased sensitivity to PI3Kα inhibitors compared to single hotspot mutations (e.g. E545K or H1047R) in experimental models and in patients with ER+ PIK3CA mutant metastatic breast cancer from the SANDPIPER randomized phase III clinical trial. These findings implicate double PIK3CA mutations in cis as a novel mechanism of oncogene addiction relative to single hotspot mutations, providing a rationale to develop PI3Kα inhibitors for the therapy of double PIK3CA mutant cancers.

Citation Format: Neil Vasan, Pedram Razavi, Jared L Johnson, Hong Shao, Timothy Wilson, Frauke Schimmoller, Hardik Shah, Alesia Antoine, Erik Ladewig, Alexander Gorelick, Ting-Yu Lin, Eneda Toska, Guotai Xu, Abiha Kazmi, Matthew T Chang, Barry S. Taylor, Maura N. Dickler, Komal Jhaveri, Sarat Chandarlapaty, Raul Rabadan, Ed Reznik, Melissa L Smith, Robert Sebra, Lori Friedman, Lewis C Cantley, Maurizio Scaltriti, José Baselga. Double PIK3CA mutations in cis drive oncogene addiction and enhance sensitivity to PI3K alpha inhibitors in breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-03-01.

Evaluating the addition of bevacizumab to endocrine therapy as first-line treatment for hormone receptor-positive metastatic breast cancer: a pooled analysis from the LEA (GEICAM/2006-11_GBG51) and CALGB 40503 (Alliance) trials

BACKGROUND

Randomised trials comparing the efficacy of standard endocrine therapy (ET) versus experimental ET + bevacizumab (Bev) in 1st line hormone receptor-positive patients with metastatic breast cancer have thus far shown conflicting results.

PATIENTS AND METHODS

We pooled data from two similar phase III randomised trials of ET ± Bev (LEA and Cancer and Leukemia Group B 40503) to increase precision in estimating treatment effect. Primary end-point was progression-free survival (PFS). Secondary end-points were overall survival (OS), objective response rate (ORR), clinical benefit rate (CBR) and safety. Exploratory analyses were performed within subgroups defined by patients with recurrent disease, de novo disease, prior endocrine sensitivity or resistance and reported grades III-IV hypertension and proteinuria.

RESULTS

The pooled sample consisted of 749 patients randomised to ET or ET + Bev. Median PFS was 14.3 months for ET versus 19 months for ET + Bev (unadjusted hazard ratio [HR] 0.77; 95% confidence interval [CI] 0.66-0.91; p < 0.01). ORR and CBR with ET and ET + Bev were 40 versus 61% (p < 0.01) and 64 versus 77% (p < 0.01), respectively. There was no difference in OS (HR 0.96; 95% CI 0.77-1.18; p = 0.68). PFS was superior for ET + Bev for endocrine-sensitive patients (HR 0.68; 95% CI 0.53-0.89; p = 0.004). Grade III-IV hypertension (2.2 versus 20.1%), proteinuria (0 versus 9.3%), cardiovascular (0.5 versus 4.2%) and liver events (0 versus 2.9%) were significantly higher for ET + Bev (all p < 0.01). Hypertension and proteinuria were not predictors of efficacy (interaction test p = 0.33).

CONCLUSION

The addition of Bev to ET increased PFS overall and in endocrine-sensitive patients but not OS at the expense of significant additional toxicity.

TRIALS REGISTRATION

ClinicalTrial.Gov NCT00545077 and NCT00601900.

Abstract 3917: Double PIK3CA mutations in cis enhance oncogene activation and sensitivity to PI3K alpha inhibitors in breast cancer

Activating mutations in PIK3CA, the gene coding for the catalytic subunit (p110α) of phosphoinositide 3-kinase (PI3K), are the most frequent oncogenic alterations in all cancers, including estrogen receptor-positive (ER+) breast cancer. There are many distinct oncogenic PIK3CA mutations including major hotspot mutations (e.g. E542K, E545K, H1047R) which are predictive of response to PI3Kα inhibitors. While responses to PI3Kα inhibitors can be variable, some patients with single hotspot mutant tumors derive a deep and prolonged clinical benefit. In a comprehensive analysis of the genomic data available in breast cancer, we observed double PIK3CA mutations and investigated their potential biological relevance and potential correlation with sensitivity to PI3Kα inhibitors. We detected double PIK3CA mutations in 10-15% of all PIK3CA-mutant cancers including breast cancer. Double PIK3CA mutations in breast cancer are defined by a pattern of co-expression of a major hotspot mutation associated with a recurrent second-site PIK3CA mutation (‘minor mutation’). We have found that these double PIK3CA mutations are compound, that is in cis on the same allele, using single molecule real time sequencing (SMRT-seq) of fresh breast tumor samples. Double compound PIK3CA mutations result in increased PI3K activity and downstream signaling compared to single hotspot mutants in nontransformed cells and in ER+ breast cancer cells. Double compound mutations also increase cell proliferation and xenograft growth compared to single hotspot mutants. Biochemical experiments using recombinant PI3K compound mutant protein complexes reveal a combination mechanism of action, with simultaneous PI3K destabilization and increased membrane binding compared to single hotspot mutants, leading to increased kinase activity. Importantly, these compound mutations predict for increased sensitivity to PI3Kα inhibitors compared to single hotspot mutants in both preclinical models and also in patients with breast cancer. Together, our data support that double compound PIK3CA mutations enhance the oncogenicity of single hotspot PIK3CA mutations and this increased dependency results in increased sensitivity to PI3Kα inhibitors compared to single hotspot mutations. We propose that double compound activating mutations are an additional mechanism of oncogenic transformation in addition to other known mechanisms such as gene amplification, point mutation, or gene translocation. We speculate that double compound mutant PIK3CA may function as a clinical biomarker of increased sensitivity to PI3K-directed targeted therapies and may improve the therapeutic window of PI3K inhibitors in ER+ breast cancer and other PIK3CA-mutant tumor histologies.

Citation Format: Neil Vasan, Pedram Razavi, Jared Johnson, Hong Shao, Hardik Shah, Alesia Antoine, Erik Ladewig, Alexander Gorelick, Eneda Toska, Guotai Xu, Abiha Kazmi, Matthew T. Chang, Barry S. Taylor, Maura N. Dickler, Komal Jhaveri, Raul Rabadan, Ed Reznik, Melissa L. Smith, Robert Sebra, Lewis C. Cantley, Maurizio Scaltriti, Jose Baselga. Double PIK3CA mutations in cis enhance oncogene activation and sensitivity to PI3K alpha inhibitors in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3917.

Clinical significance of circulating tumor cells (CTCs) in hormone receptor-positive (HR+) metastatic breast cancer (MBC) patients (pts) receiving letrozole (Let) or Let plus bevacizumab (Bev): CALGB 40503 (Alliance)

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Background: CALGB 40503 randomized HR+ MBC postmenopausal pts to Let alone or Let+Bev as first-line therapy. Adding Bev to Let prolonged progression-free survival (PFS) but not overall survival (OS) (Dickler JCO 2016). We performed a correlative study to assess prognostic and predictive value of CTCs in this population. Methods: Blood was collected prior to initiation of treatment. CTCs were enumerated using US FDA-cleared CellSearch assay; samples with ≥5 CTCs per 7.5 mLs of blood were considered CTC-positive (CTC+). Correlation of CTCs with PFS and OS was assessed using Cox regression analysis. Median follow-up was 39 months (mo). Results: Of 343 pts treated, 294 had CTC data and were included in this analysis. Original study results that showed improved PFS (HR = 0.75; 95% CI: 0.59-0.96) but not OS (HR = 0.87; 95% CI: 0.65-1.18) in pts receiving Let+Bev compared to Let were recapitulated in this subset. In multivariable analysis, CTC+ pts (31%) had significantly reduced PFS (HR = 1.49; 95% CI: 1.12-1.97) and OS (HR = 2.08; 95% CI: 1.49-2.93) compared to CTC- pts. Moreover, CTC+ pts who did not receive Bev had worse PFS (HR = 2.31; 95% CI: 1.54-3.47) and OS (HR = 2.64; 95% CI: 1.59-4.40) (Table). CTC+ pts who received Bev had numerically longer median PFS (18.0 vs. 7.0 mo) and OS (33.6 vs. 27.1 mo) compared to CTC+ pts with no Bev; however, tests for interaction between CTC status and Bev (yes vs. no) were not statistically significant for PFS (p=0.70) or OS (p=0.84). Conclusions: CTCs were highly prognostic in this study involving addition of Bev to first-line Let in postmenopausal HR+ MBC. Further research to determine the potential predictive value of CTCs in the setting of both metastatic disease and early breast cancer is warranted. Support: U10CA180821, U10CA180882; Genentech; https://acknowledgments.alliancefound.org ; NCT00601900. Survival in HR+ MBC pts receiving Let or Let+Bev stratified by CTC status. Clinical trial information: NCT00601900. [Table: see text]

Abstract PD6-06: Impact of BRCA mutations on chemotherapy-induced loss of ovarian reserve: A prospective longitudinal study

Background: The BRCA1/2 genes are key members of the ataxia-telangiectasia mutated (ATM)-mediated DNA double strand break (DSB) repair pathway. Recent research showed that germline mutations in these genes result in DNA repair deficiency in oocytes, leading to accelerated ovarian aging as manifested by lower ovarian reserve and earlier age at natural menopause. Because we discovered that oocyte DNA repair is similarly critical in chemotherapy-induced ovarian follicle loss, we hypothesized that women with pathogenic mutations in BRCA1/2 genes may experience larger declines in ovarian reserve after chemotherapy. To gauge the degree of the chemotherapy-induced ovarian damage, we utilized serum anti-mullerian hormone (AMH), which is the most reliable current marker for assessing oocyte reserve.

Methods: Women with early stage breast cancer were enrolled before chemotherapy (Trial registration number: NCT00823654) between January 2009 and November 2017. Sera were obtained at baseline, before the initiation of treatment, and 18 to 24 months after the completion of chemotherapy. Stored sera were assayed at once for anti-mullerian hormone (AMH) and the results were adjusted for the women's age at sample collection. Of the 235 enrolled, 117 evaluable women were stratified into three groups, those never tested (based on NCCN Guidelines V 1.2018 ; n=38) and those negative (n=65) or positive (n=14) for a pathogenic BRCA mutation. Ovarian recovery was defined as the geometric mean of the post chemotherapy age-adjusted AMH levels compared to baseline.

Results: Compared to the lower risk (BRCA-untested) control group, AMH levels averaged 76% and 66% in those negative or positive for BRCA mutations (p=0.078). The geometric mean recoveries for the three groups (not tested, BRCA negative and BRCA positive) were 3.7%, 5.2% and 1.6%, respectively. The mean recovery in the BRCA mutation positive group was about one-third the 4.6% recovery in the other two groups combined (two group ANOVA, p=0.034, F=4.89). Given the potential of the ovarian recovery to be dependent on type of chemotherapy, the data were reanalyzed for all three BRCA groups after restriction to those treated with the AC-T (doxorubicin and cyclophosphamide followed by paclitaxel) regimen. Of the 108 women in the previous analysis, 83 (77%) were treated with AC-T; 25, 46 and 12 women in the three groups, respectively. The geometric mean AMH recoveries for these new groups were 3.2%, 4.7% and 1.3%. When the BRCA mutation positive group was compared with other two groups, the former had significantly worse recovery of serum AMH levels (ANOVA, p=0.044, F=4.2).

Conclusions: These data show that women with breast cancer and pathogenic BRCA mutations have striking liability to chemotherapy-induced ovarian reserve loss and may have to be preferentially counselled on fertility preservation methods. In addition, taken together with the previous data showing that women with BRCA mutations may have accelerated ovarian aging, even unaffected reproductive age individuals may have to be proactive about family building or early preservation of their fertility (Supported by NIH R01HD053112).

Citation Format: Oktay K, Bedoschi G, Goldfarb SB, Taylan E, Titus S, Palomaki GE, Cigler T, Robson M, Dickler MN. Impact of BRCA mutations on chemotherapy-induced loss of ovarian reserve: A prospective longitudinal study [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD6-06.

Abstract P2-07-05: A clinical calculator to predict disease outcomes in women with hormone receptor-positive advanced stage breast cancer treated with first-line endocrine therapy

Purpose: Endocrine based therapy is an effective strategy to manage hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC). However, nearly all patients exhibit/develop either de novo or acquired resistance. While prognostic biomarkers of endocrine responsiveness are well established for the adjuvant treatment in ER+ breast cancer, less is known regarding prognostic and predictive biomarkers of response in the first line ABC setting. We sought to develop a clinical calculator based on clinical criteria for predicting progression-free survival (PFS) and overall survival (OS) of women with HR+/HER2- ABC who will be receiving endocrine monotherapy as first-line treatment for ABC.

Methods: The development of the clinical calculator will be based on data from modern clinical trials in women with HR+/HER2- ABC. The studies to be included in the final analyses are given in Table 1. The control arm data from trials1-6 will form the training dataset (N = 1,223) and be used to construct the clinical prediction models. Variables considered include age, race, ECOG status, disease measurability, body mass index, disease-free interval, number of metastatic sites, locations of metastatic sites, prior endocrine therapy, and prior chemotherapy. Missing values will be imputed using single imputation with all variables included in the imputation model. For continuous variables, restricted cubic splines will be used to determine if non-linear effects may be more appropriate. The Lasso regression will be used as a variable selection technique to reduce the dimensionality of covariates; initially all pairwise interactions will be included in the model. Following Lasso regression, the multivariable Cox proportional hazards models will be constructed for PFS and OS including only variables retained in Lasso. The final model will be internally validated for discrimination and calibration using 10-fold cross-validation. External validation will be performed using control arm data from EGF 30008 (N = 536).

Results: To date, control arm data from four trials (trials 1-4) have been received. The preliminary results presented here are based on pooled data from C40503 and LEA, for which data elements have been harmonized. Models for predicting PFS and OS have good calibration and are associated with bias-corrected C-indices of 0.61 and 0.65, respectively. These models will be updated using pooled data from trials 1-6.

Conclusions: Our preliminary data demonstrate that clinical calculators based on baseline clinical factors can provide accurate prediction of PFS and OS in patients with HR+/HER2- ABC treated with first-line ET. If validated, these tools may be used for risk stratification in future clinical trials and to identify patients who may require more or less aggressive therapy.

Table 1:Studies to be includedTrial NumberTrial NameTrial PISample Size in Control Arm1C40503Maura Dickler152 (letrozole)2LEAMiguel Martin179 (letrozole)3FACTJonas Bergh188 (anastrozole)4FALCONJohn Robertson194 (anastrozole)5S0226Rita Mehta345 (anastrozole)6MONARCH 3Matthew Goetz165 (nonsteroidal AI)7EGF 30008Stephen Johnston536 (letrozole)

Citation Format: Polley M-YC, Dickler MN, Johnston S, Goetz MP, de la Haba J, Loibl S, Mehta RS, Bergh J, Roberston J, Barlow W, Liu H, Tenner K, Martin M. A clinical calculator to predict disease outcomes in women with hormone receptor-positive advanced stage breast cancer treated with first-line endocrine therapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-07-05.

Abstract P6-18-19: Real-world survival of heavily pretreated patients with refractory HR+, HER2- metastatic breast cancer receiving single-agent chemotherapy - A comparison with MONARCH 1

Background

In MONARCH 1 (NCT02102490), abemaciclib demonstrated promising single-agent activity and tolerability in a population of heavily pretreated women with refractory HR+, HER2- metastatic breast cancer (MBC).1 Confirmed objective response rate (ORR) was 19.7% (95% CI: 13.3, 27.5) and at 18 months minimum follow-up median overall survival (OS) was 22.3 months. Due to the single-arm trial design of MONARCH 1, there is a need to view these results in clinical context relative to available treatment options. This study compared the OS results of abemaciclib in MONARCH 1 vs that in a real-world single-agent chemotherapy cohort with similar patient and disease characteristics.

Methods

MONARCH 1 study design and key eligibility criteria were previously described.1 The real-world cohort was based on Flatiron Health electronic health records-derived, nationally representative (USA-based) database comprising patient-level structured and unstructured data, curated via technology-enabled abstraction, for patients with MBC between January 1, 2011 through February 28, 2018. A real-world single-agent chemotherapy cohort was created based on the key eligibility criteria of MONARCH 1 and included patients diagnosed with HR+, HER2- MBC who received single-agent chemotherapy (eribulin, capecitabine, gemcitabine, or vinorelbine) following 1-2 prior chemotherapy regimens in the metastatic setting, had an ECOG PS of 0-1, and no prior CDK4 & 6 therapy. The index date was the start of the eligible single-agent chemotherapy, and patients were followed from the index date until date of death, loss to follow-up, or end of the database, whichever occurred earlier. OS results were adjusted using 2 methods (Mahalanobis distance matching and entropy balancing with bootstrapping) to account for baseline demographic and clinical differences between the real-world and trial cohorts.

Results

A real-world cohort (n=281) with eligibility criteria similar to the MONARCH 1 population (n=132) was identified. A subsequent matching based on Mahalanobis distance was performed to match MONARCH 1 population (n=108) with the real-world cohort (n=108). The matched cohorts demonstrated similar patient and disease characteristics. Median OS was 22.3 months in the abemaciclib arm vs 13.6 months in the matched cohort with an estimated hazard ratio (HR) of 0.54 (95% CI: 0.37, 0.77). Results of a sensitivity analysis performed using entropy balancing were consistent with an adjusted median OS of 12.7 months in the real-world cohort (n=281)with HR of 0.57 (95% CI from bootstrapping: 0.44, 0.78).

Conclusion

Methodological advances to adjust for potential biases, and improvements in data quality, have evolved enabling the ability to leverage a real-world cohort as an external comparator arm. This study demonstrates the ability to create a real-world chemotherapy cohort suitable to serve as a comparator for MONARCH 1. These exploratory results suggest a survival advantage and adequately place the clinical benefit of abemaciclib monotherapy in clinical context.

References

Dickler et al, CCR 2017

Citation Format: Rugo H, Dieras V, Cortes J, Patt D, Wildiers H, O'Shaughnessy J, Zamora E, Yardley DY, Carter GC, Sheffield KM, Li L, Andre VA, Derbyshire RE, Li XI, Frenzel M, Huang Y-J, Dickler MN, Tolaney SM. Real-world survival of heavily pretreated patients with refractory HR+, HER2- metastatic breast cancer receiving single-agent chemotherapy - A comparison with MONARCH 1 [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-18-19.

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

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

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

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

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

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

The Genomic Landscape of Endocrine-Resistant Advanced Breast Cancers

We integrated the genomic sequencing of 1,918 breast cancers, including 1,501 hormone receptor-positive tumors, with detailed clinical information and treatment outcomes. In 692 tumors previously exposed to hormonal therapy, we identified an increased number of alterations in genes involved in the mitogen-activated protein kinase (MAPK) pathway and in the estrogen receptor transcriptional machinery. Activating ERBB2 mutations and NF1 loss-of-function mutations were more than twice as common in endocrine resistant tumors. Alterations in other MAPK pathway genes (EGFR, KRAS, among others) and estrogen receptor transcriptional regulators (MYC, CTCF, FOXA1, and TBX3) were also enriched. Altogether, these alterations were present in 22% of tumors, mutually exclusive with ESR1 mutations, and associated with a shorter duration of response to subsequent hormonal therapies.

Feasibility, safety, and efficacy of aerobic training in pretreated patients with metastatic breast cancer: A randomized controlled trial

BACKGROUND

The investigation of exercise training in metastatic breast cancer has received minimal attention. This study determined the feasibility and safety of aerobic training in metastatic breast cancer.

METHODS

Sixty-five women (age, 21-80 years) with metastatic (stage IV) breast cancer (57% were receiving chemotherapy, and >40% had ≥ 2 lines of prior therapy) were allocated to an aerobic training group (n = 33) or a stretching group (n = 32). Aerobic training consisted of 36 supervised treadmill walking sessions delivered thrice weekly between 55% and 80% of peak oxygen consumption (VO2peak ) for 12 consecutive weeks. Stretching was matched to aerobic training with respect to location, frequency, duration, and intervention length. The primary endpoint was aerobic training feasibility, which was a priori defined as the lost to follow-up (LTF) rate (<20%) and attendance (≥70%). Secondary endpoints were safety, objective outcomes (VO2peak and functional capacity), and patient-reported outcomes (PROs; quality of life).

RESULTS

One of the 33 patients (3%) receiving aerobic training was LTF, whereas the mean attendance rate was 63% ± 30%. The rates of permanent discontinuation and dose modification were 27% and 49%, respectively. Intention-to-treat analyses indicated improvements in PROs, which favored the attention control group (P values > .05). Per protocol analyses indicated that 14 of 33 patients (42%) receiving aerobic training had acceptable tolerability (relative dose intensity ≥ 70%), and this led to improvements in VO2peak and functional capacity (P values < .05).

CONCLUSIONS

Aerobic training at the dose and schedule tested is safe but not feasible for a significant proportion of patients with metastatic breast cancer. The acceptable feasibility and promising benefit for select patients warrant further evaluation in a dose-finding phase 1/2 study. Cancer 2018;124:2552-60. © 2018 American Cancer Society.

Phase II Study of Taselisib (GDC-0032) in Combination with Fulvestrant in Patients with HER2-Negative, Hormone Receptor-Positive Advanced Breast Cancer

Purpose: This single-arm, open-label phase II study evaluated the safety and efficacy of taselisib (GDC-0032) plus fulvestrant in postmenopausal women with locally advanced or metastatic HER2-negative, hormone receptor (HR)-positive breast cancer.Patients and Methods: Patients received 6-mg oral taselisib capsules daily plus intramuscular fulvestrant (500 mg) until disease progression or unacceptable toxicity. Tumor tissue (if available) was centrally evaluated for PIK3CA mutations. Adverse events (AE) were recorded using NCI-CTCAE v4.0. Tumor response was investigator-determined using RECIST v1.1.Results: Median treatment duration was 4.6 (range: 0.9-40.5) months. All patients experienced ≥1 AE, 30 (50.0%) had grade ≥3 AEs, and 19 (31.7%) experienced 35 serious AEs. Forty-seven of 60 patients had evaluable tissue for central PIK3CA mutation testing [20 had mutations, 27 had no mutation detected (MND)]. In patients with baseline measurable disease, clinical activity was observed in tumors with PIK3CA mutations [best confirmed response rate: 38.5% (5/13; 95% CI, 13.9-68.4); clinical benefit rate (CBR): 38.5% (5/13; 95% CI, 13.9-68.4)], PIK3CA-MND [best confirmed response rate: 14.3% (3/21; 95% CI, 3.0-36.3); CBR: 23.8% (5/21; 95% CI, 8.2-47.2)], and unknown PIK3CA mutation status [best confirmed response rate: 20.0% (2/10; 95% CI, 2.5-55.6); CBR: 30.0% (3/10; 95% CI, 6.7-65.2)].Conclusions: Taselisib plus fulvestrant had clinical activity irrespective of PIK3CA mutation status, with numerically higher objective response rate and CBR in patients with PIK3CA-mutated (vs. -MND) locally advanced or metastatic HER2-negative, HR-positive breast cancer. No new safety signals were reported. A confirmatory phase III trial is ongoing. Clin Cancer Res; 24(18); 4380-7. ©2018 AACR.

Abstract PD5-10: A first-in-human phase I study to evaluate the oral selective estrogen receptor degrader (SERD), GDC-0927, in postmenopausal women with estrogen receptor positive (ER+) HER2-negative metastatic breast cancer (BC)

Background: Modulation of estrogen activity and/or synthesis is the mainstay therapeutic strategy in the treatment of ER+ BC. However, despite the effectiveness of available endocrine therapies, many patients ultimately relapse or develop resistance to these agents via estrogen-dependent and estrogen-independent mechanisms, including mutations in ESR1 affecting the ER ligand binding domain that drive ER-dependent transcription and proliferation in the absence of estrogen. ER antagonists that are efficacious against ligand-dependent and ligand-independent, constitutively active ESR1 mutant tumors may be of substantial therapeutic benefit. GDC-0927 (formerly known as SRN-927) is a novel, potent, non-steroidal, orally bioavailable, selective ER antagonist/ER degrader (SERD) that induces tumor regression in ER+ BC patient-derived xenograft models.

Methods: A phase I dose escalation study with 3+3 design was conductedin postmenopausal women with ER+ (HER2-) metastatic BC (progressing ≥ 6 months on endocrine therapy and with ≤ 2 prior chemotherapies in the advanced or metastatic setting) to determine the safety, pharmacokinetics (PK) and the recommended Phase 2 dose (RP2D) of GDC-0927. Pharmacodynamic (PD) activity was assessed with [18F]-fluoroestradiol (FES)-PET scans. Plasma PK samples (after single dose and at steady state), CT scans, and when feasible, pre and on-study tumor biopsies were obtained

Results: From March 16, 2015 to March 17, 2017 patients (pts) with a median age of 53 years (range 44-69) and a median number of prior therapies for MBC 4 (range 1-7) were enrolled at 3 total daily dose levels (600, 1000, 1400 mg) once daily (QD) given orally with fasting (n = 12). Increases in GDC-0927 exposure were approximately dose proportional. Treatment related adverse events (AEs) were all grade 1 or 2. The most common treatment-related AEs were nausea (54%, n = 7), diarrhea (46%, n = 6), elevated aspartate aminotransferase (39%, n = 5) and anemia, constipation, (each 31%, n = 4). Treatment interruption was required for 2 pts due to nausea and vomiting. Of those pts with FES-PET avid disease at baseline (9 of 12), all post-therapy scans showed complete or near complete (&gt; 90%) suppression of FES uptake to background levels, including pts with ESR1 mutations. Evidence of reduced ER levels and Ki67 staining was observed in on-treatment biopsies. Five of 12 pts (1 at 600 mg and 4 at 1400 mg) were on study ≥ 24 weeks (CBR = 41.6 %) with the best overall response of stable disease with 1 patient (ESR1 mt+ D538G) on study for over 490 days. There were no dose limiting toxicities and no SAEs related to study drug. R2PD was 1400 mg and was selected for single arm dose-expansion which is now complete with last patient enrolled on March 17, 2017. Updated results from dose-escalation and dose-expansion will be presented at the meeting (N = 43).

Conclusions: GDC-0927 appears well-tolerated to date with PK exposure supporting QD dosing, evidence of robust PD target engagement, and encouraging anti-tumor activity in heavily pretreated pts with advanced or metastatic ER+ BC, including pts with ESR1 mutations.

Citation Format: Dickler MN, Villanueva R, Perez Fidalgo JA, Mayer IA, Boni V, Winer EP, Hamilton EP, Bellet M, Urruticoechea A, Gonzalez-Martin A, Cortes J, Martin M, Giltnane J, Gates M, Cheeti S, Fredrickson J, Wang X, Friedman LS, Spoerke JM, Metcalfe C, Liu L, Li R, Morley R, McCurry U, Chan IT, Mueller L, Milan S, Lauchle J, Humke EW, Bardia A. A first-in-human phase I study to evaluate the oral selective estrogen receptor degrader (SERD), GDC-0927, in postmenopausal women with estrogen receptor positive (ER+) HER2-negative metastatic breast cancer (BC) [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 PD5-10.

Estrogen Receptor-Positive Breast Cancer: Exploiting Signaling Pathways Implicated in Endocrine Resistance

Advancements in molecular profiling and endocrine therapy (ET) have led to more focused clinical attention on precision medicine. These advances have expanded our understanding of breast cancer (BC) pathogenesis and hold promising implications for the future of therapy. The estrogen receptor-α is a predominant endocrine regulatory protein in the breast and in estrogen-induced BC. Successful targeting of proteins and genes within estrogen receptor (ER) nuclear and nonnuclear pathways remains a clinical goal. Several classes of antiestrogenic agents are available for patients with early, advanced, or metastatic BC, including selective ER modulators, aromatase inhibitors, and a selective ER degrader. Clinical development is focused upon characterizing the efficacy and tolerability of inhibitors that target the phosphatidylinositol 3 kinase (PI3K)/akt murine thymoma viral oncogene (AKT)/mammalian target of rapamycin inhibitor (mTOR) signaling pathway or the cyclin-dependent kinase 4/6 (CDK4/6) cell cycle pathway in women with hormone receptor-positive, human epidermal growth receptor 2-negative BC who have demonstrated disease recurrence or progression. De novo and acquired resistance remain a major challenge for women with BC receiving antiestrogenic therapy. Therefore, sequential combination of targeted ET is preferred in these patients, and the ever-increasing understanding of resistance mechanisms may better inform the selection of future therapy. This review describes the intricate roles of the PI3K/AKT/mTOR and CDK4/6 pathways in intracellular signaling and the use of endocrine and endocrine-based combination therapy in BC.

IMPLICATIONS FOR PRACTICE

The foundational strategy for treating hormone receptor-positive, human epidermal growth receptor 2-negative, advanced breast cancer includes the use of endocrine therapy either alone or in combination with targeted agents. The use of combination therapy aims to downregulate cell-signaling pathways with the intent of minimizing cellular "crosstalk," which can otherwise result in continued tumorigenesis or progression through redundant pathways. This review provides the clinician with the molecular rationale and clinical evidence for these treatments and refers to evidence-based guidelines to inform the decision-making process.

Mutation Detection in Patients With Advanced Cancer by Universal Sequencing of Cancer-Related Genes in Tumor and Normal DNA vs Guideline-Based Germline Testing

IMPORTANCE

Guidelines for cancer genetic testing based on family history may miss clinically actionable genetic changes with established implications for cancer screening or prevention.

OBJECTIVE

To determine the proportion and potential clinical implications of inherited variants detected using simultaneous sequencing of the tumor and normal tissue ("tumor-normal sequencing") compared with genetic test results based on current guidelines.

DESIGN, SETTING, AND PARTICIPANTS

From January 2014 until May 2016 at Memorial Sloan Kettering Cancer Center, 10 336 patients consented to tumor DNA sequencing. Since May 2015, 1040 of these patients with advanced cancer were referred by their oncologists for germline analysis of 76 cancer predisposition genes. Patients with clinically actionable inherited mutations whose genetic test results would not have been predicted by published decision rules were identified. Follow-up for potential clinical implications of mutation detection was through May 2017.

EXPOSURE

Tumor and germline sequencing compared with the predicted yield of targeted germline sequencing based on clinical guidelines.

MAIN OUTCOMES AND MEASURES

Proportion of clinically actionable germline mutations detected by universal tumor-normal sequencing that would not have been detected by guideline-directed testing.

RESULTS

Of 1040 patients, the median age was 58 years (interquartile range, 50.5-66 years), 65.3% were male, and 81.3% had stage IV disease at the time of genomic analysis, with prostate, renal, pancreatic, breast, and colon cancer as the most common diagnoses. Of the 1040 patients, 182 (17.5%; 95% CI, 15.3%-19.9%) had clinically actionable mutations conferring cancer susceptibility, including 149 with moderate- to high-penetrance mutations; 101 patients tested (9.7%; 95% CI, 8.1%-11.7%) would not have had these mutations detected using clinical guidelines, including 65 with moderate- to high-penetrance mutations. Frequency of inherited mutations was related to case mix, stage, and founder mutations. Germline findings led to discussion or initiation of change to targeted therapy in 38 patients tested (3.7%) and predictive testing in the families of 13 individuals (1.3%), including 6 for whom genetic evaluation would not have been initiated by guideline-based testing.

CONCLUSIONS AND RELEVANCE

In this referral population with selected advanced cancers, universal sequencing of a broad panel of cancer-related genes in paired germline and tumor DNA samples was associated with increased detection of individuals with potentially clinically significant heritable mutations over the predicted yield of targeted germline testing based on current clinical guidelines. Knowledge of these additional mutations can help guide therapeutic and preventive interventions, but whether all of these interventions would improve outcomes for patients with cancer or their family members requires further study.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01775072.

Abstract CT044: MONARCH 1: Final overall survival analysis of a phase 2 study of abemaciclib, a CDK4 and CDK6 inhibitor, as monotherapy, in patients with HR+/HER2- breast cancer, after chemotherapy for advanced disease

Background: Abemaciclib is an oral, selective inhibitor of CDK4 and CDK6 dosed on a continuous schedule. MONARCH 1 (NCT02102490) is a phase 2 single-arm study designed to evaluate safety and efficacy of abemaciclib monotherapy in women with HR+/HER2- MBC whose disease progressed on or after endocrine therapy and chemotherapy. Final analysis of the primary endpoint, objective response rate (ORR) at 12 months (mo), showed that abemaciclib monotherapy induced objective tumor responses in patients (pts) with refractory HR+/HER2- MBC following multiple prior therapies. Treatment was well tolerated, allowing prolonged exposure to therapy. We report the final 18 mo overall survival results.

Methods: Eligible pts had measurable disease, ECOG PS of 0/1, no CNS metastases, and received at least 1 but no more than 2 lines of chemotherapy in the metastatic setting. Abemaciclib (200 mg) was administered orally on a continuous schedule every 12 hours until disease progression. The primary objective was to evaluate ORR per RECIST v1.1. at 12 mo after the last pt enrolled. Secondary objectives included duration of response (DoR), progression-free survival (PFS), overall survival (OS), disease control rate (DCR = CR + PR + SD), clinical benefit rate (CBR= CR + PR + SD ≥ 6 mo) and safety. Final OS analysis occurred 18 mo after the last pt was enrolled.

Results: A total of 132 pts received abemaciclib monotherapy. The primary endpoint of ORR by investigator assessment at 12 mo was 19.7% (95% CI: 13.3, 27.5) and did not change at 18 mo. Of the 26 responding pts, 19 (73.1%) had responses ≥ 6 mo, and 6 pts still on treatment have response durations ranging from 9.5+ to 20.5+ mo. There was no change at 18 mo vs 12 mo for DCR (67.4%) or CBR (42.4%). Median PFS (6.0 mo, 95% CI: 4.2, 7.5) and median DoR (8.9 mo, 95% CI: 6.1, 14.0) were also consistent with 12 mo follow up. At the 18 mo update, 7 pts (5.3%) remained on treatment (6 PR and 1 SD). At 18 mo, the median OS was 22.3 mo (95% CI: 17.7, NR), and the survival rate was 58.7%. TEAEs ≥ Grade 3 were experienced by 93 pts (70.5%) at 18 mo, compared to 90 pts (68.2%) at 12 mo. The most common Grade 3/4 TEAEs were neutropenia (25.0%), diarrhea (19.7%), fatigue (13.6%), leukopenia (6.8%), anemia (4.5%) and nausea (4.5%). Treatment discontinuations due to AEs were infrequent (7.6 %).

Conclusions: The results of the 18 month analysis are consistent with the 12 month results of MONARCH 1. Median OS was 22.3 months. The efficacy results from the MONARCH 1 study indicate that continuous administration of single-agent abemaciclib induces durable confirmed tumor responses. There were no clinically significant changes in safety. The results of the 18 month analysis support the earlier results and indicate that single-agent abemaciclib may offer a more favorable benefit-risk profile than expected from available cytotoxic chemotherapies.

Citation Format: Hope S. Rugo, Sara M. Tolaney, Javier Cortés, Véronique Diéras, Debra A. Patt, Hans Wildiers, Shivani Nanda, Andrew G. Koustenis, Maura N. Dickler, José Baselga. MONARCH 1: Final overall survival analysis of a phase 2 study of abemaciclib, a CDK4 and CDK6 inhibitor, as monotherapy, in patients with HR+/HER2- breast cancer, after chemotherapy for advanced disease [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT044. doi:10.1158/1538-7445.AM2017-CT044

MONARCH 1, A Phase II Study of Abemaciclib, a CDK4 and CDK6 Inhibitor, as a Single Agent, in Patients with Refractory HR+/HER2- Metastatic Breast Cancer

Purpose: The phase II MONARCH 1 study was designed to evaluate the single-agent activity and adverse event (AE) profile of abemaciclib, a selective inhibitor of CDK4 and CDK6, in women with refractory hormone receptor-positive (HR⁺), HER2^- metastatic breast cancer (MBC).Experimental Design: MONARCH 1 was a phase II single-arm open-label study. Women with HR⁺/HER2^- MBC who had progressed on or after prior endocrine therapy and had 1 or 2 chemotherapy regimens in the metastatic setting were eligible. Abemaciclib 200 mg was administered orally on a continuous schedule every 12 hours until disease progression or unacceptable toxicity. The primary objective of MONARCH 1 was investigator-assessed objective response rate (ORR). Other endpoints included clinical benefit rate, progression-free survival (PFS), and overall survival (OS).Results: Patients (n = 132) had a median of 3 (range, 1-8) lines of prior systemic therapy in the metastatic setting, 90.2% had visceral disease, and 50.8% had ≥3 metastatic sites. At the 12-month final analysis, the primary objective of confirmed objective response rate was 19.7% (95% CI, 13.3-27.5; 15% not excluded); clinical benefit rate (CR+PR+SD≥6 months) was 42.4%, median progression-free survival was 6.0 months, and median overall survival was 17.7 months. The most common treatment-emergent AEs of any grade were diarrhea, fatigue, and nausea; discontinuations due to AEs were infrequent (7.6%).Conclusions: In this poor-prognosis, heavily pretreated population with refractory HR⁺/HER2^- metastatic breast cancer, continuous dosing of single-agent abemaciciclib was well tolerated and exhibited promising clinical activity. Clin Cancer Res; 23(17); 5218-24. ©2017 AACR.

Evaluating the addition of bevacizumab (Bev) to endocrine therapy as first-line treatment for hormone-receptor positive (HR+)/HER2-negative advanced breast cancer (ABC): Pooled-analysis from the LEA (GEICAM/2006-11_GBG51) and CALGB 40503 (Alliance) trials

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Background: Data from randomized trials comparing ET v ET-Bev in 1st line HR+/HER2- ABC pts showed controversial results. We performed a pooled-analysis of two randomized trials (LEA and CALGB 40503) to refine the Bev value in this patient population. Methods: We analysed 749 ABC pts with ET (letrozole-673, tamoxifen-39, fulvestrant 250mg-37) +/- Bev. Primary objective was to compare progression-free survival (PFS). Secondary endpoints were: safety; other efficacy (overall response rate [ORR], clinical benefit rate [CBR] and overall survival [OS]) in all pts; and efficacy in de novo pts and by previous endocrine-sensitivity (-/+ 24 months [mo] without recurrence under ET in adjuvant setting). Multivariable Cox models were fitted for PFS adjusted by study co-variables and controlled for study level differences. Results: Median age was 61 years (yr) (range: 25-87); 40% had de novo ABC and 60% recurrent disease (with disease free interval of ≤ 1 yr in 5%, 1-2 yr in 7% and > 2 yr in 88%); 82% of recurrent pts had previous ET sensitivity. Median PFS was 14.3 mo in the ET arm v 19 mo in the ET+Bev arm (HR 0.77; 95% CI 0.66-0.91; p<0.01). ORR and CBR with ET v ET+Bev were 40 v 61% (p<0.01) and 64 v 77% (p<0.01). OS did not differ between arms (HR 0.96; 95% CI 0.77-1.18; p=0.68). PFS for de novo ABC pts was 14.6 and 19.3 mo in the ET and ET+Bev arms (HR 0.82; 95% CI 0.63-1.06; p=0.13). PFS differed between arms for previous sensitive pts (HR 0.68; 95% CI 0.53-0.89; p=0.004) but not for ET-resistant pts (HR 0.73; 95% CI 0.4-1.3; p=0.29). Grade 3-5 hypertension (2.2 v 20.1%), proteinuria (0 v 9.3%), cardiovascular events (0.5 v 4.2%) and liver events (0 v 2.9%) were significantly higher in the ET+Bev arm (all p<0.01). Multivariable analyses showed age (p<0.01), PgR status (p<0.01), type of prior ET (p<0.01) and treatment arm (p<0.01) to be associated with PFS. Conclusions: The addition of Bev to ET increased PFS but not OS. Analyses to define subgroups with prolonged benefit from ET alone or ET-Bev are ongoing. Support: U10CA180821, U10CA180882, Breast Cancer Research Foundation, Genentech, Roche. Clinical trial information: NCT00545077 / NCT00601900.

Surgical ovarian ablation for hormone receptor positive primary breast cancer in premenopausal women

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Background: Ovarian ablation is increasingly used to complement endocrine therapy in select premenopausal women with hormone-receptor positive (HR+) breast cancer (BC). It can be achieved by either medical ovarian suppression (OS) or therapeutic bilateral salpingo-oophorectomy (BSO). We sought to investigate trends of therapeutic BSO in premenopausal patients at our institution. Methods: Premenopausal women with HR+ primary BC diagnosed from 2010-2014 were identified in our prospectively maintained BC database. Patients with confirmed BRCA1/2 mutations were excluded. Distribution of patient and disease characteristics between treatment groups were assessed using univariate logistic regression analyses. Surgical details and complications were extracted from our surgical database. Results: We identified 2,854 eligible patients; 2,113 (74%) received endocrine therapy without ovarian ablation, 246 (9%) received endocrine therapy plus medical OS, 180 (6%) underwent additional BSO, and 315 (11%) did not receive endocrine therapy at the time of analysis. Independent predictors for undergoing ovarian ablation were younger age (OR 0.98; 95%CI, 0.96-0.99; p < 0.001), higher grade (grade 3 vs 1: OR 3.17; 95%CI, 1.70-5.90; grade 2 vs 1: OR 3.13; 95%CI, 1.64-5.95; p < 0.001), lymph node involvement (OR 1.46; 95%CI, 1.19-1.80; p < 0.001), and higher AJCC stage as well as de novo metastatic BC (II vs I: OR = 1.35; 95%CI, 1.03-1.76; III vs I: OR 2.57; 95%CI, 1.86-3.55; IV vs I: OR 19.69; 95%CI, 12.76-30.39; p < 0.001). Among patients who underwent ovarian ablation, patients of younger age (1.04; 95%CI, 1.01-1.07; p = 0.009) and with metastatic BC (stage IV vs I: OR 0.36; 95%CI, 0.20-0.68; p = 0.007) were less likely to undergo BSO than OS. In 180 patients undergoing BSO, five adverse events were noted: two grade 1, two grade 2, and one grade 3 complication. Conclusions: Premenopausal women with HR+ BC with high-risk features or metastatic disease were more likely to undergo ovarian ablation at our institution. Surgical ovarian ablation is a safe alternative, with low complication rates. Understanding patient preferences, side effects, and quality of life implications will help guide personalized treatment decisions.

Phase II study of gemcitabine (G), trastuzumab (H), and pertuzumab (P) for HER2-positive metastatic breast cancer (MBC) after prior pertuzumab-based therapy

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Background: The combination of taxanes with HP for first line treatment of HER2-positive MBC is associated with improved progression-free (PFS) and overall survival (OS). Treatment per physician’s choice with anti-HER2 therapy after second line therapy is associated with a median PFS of 3 months. While continued use of H in therapeutic combinations after progression on H-based therapy is standard, the efficacy of continuing HP-based treatment after progression on P-based therapy is unknown. Methods: This is a single arm phase II trial of G with HP. Eligible patients (pts) had HER2-positive (IHC 3+ or FISH > 2.0) MBC with prior HP-based treatment and ≤ 3 prior chemotherapies. Pts received G (1200 mg/m2) on days 1 and 8 of a q 3 week (w) cycle, and H (8 mg/kg load → 6 mg/kg) and P (840 mg load → 420 mg) q3w. The primary endpoint is PFS at 3 months. Secondary endpoints include OS, safety and tolerability. An exploratory endpoint is to compare PFS by RECIST criteria versus 18-F FDG-PET response criteria. The study therapy will be considered successful if at least 27/45 (60%) patients are progression free at 3 months. Results: As of 1-27-17, 41 of 45 pts are enrolled; 34 are evaluable at 3 months and 7 have not had 3-month evaluation. At 3 months, 26/34 (76%) are progression free (1 CR, 8 PR, 17 SD); 8 pts progressed. There are no cardiac or febrile neutropenic events to date. 4 pts required G dose reduction (3 grade 3 neutropenia and 1 grade 3 vomiting) and the study was amended to lower initial G dose to 1000 mg/m2. Conclusions: The preliminary 3 month-PFS is 76% in evaluable pts (95% CI 60% to 88%). The updated 3 month-PFS results will be presented. Continuation of P beyond progression is associated with apparent clinical benefit. A randomized trial is justified to confirm this clinically important observation. Clinical trial information: NCT02252887.

PI3K pathway regulates ER-dependent transcription in breast cancer through the epigenetic regulator KMT2D

Activating mutations in PIK3CA, the gene encoding phosphoinositide-(3)-kinase α (PI3Kα), are frequently found in estrogen receptor (ER)-positive breast cancer. PI3Kα inhibitors, now in late-stage clinical development, elicit a robust compensatory increase in ER-dependent transcription that limits therapeutic efficacy. We investigated the chromatin-based mechanisms leading to the activation of ER upon PI3Kα inhibition. We found that PI3Kα inhibition mediates an open chromatin state at the ER target loci in breast cancer models and clinical samples. KMT2D, a histone H3 lysine 4 methyltransferase, is required for FOXA1, PBX1, and ER recruitment and activation. AKT binds and phosphorylates KMT2D, attenuating methyltransferase activity and ER function, whereas PI3Kα inhibition enhances KMT2D activity. These findings uncover a mechanism that controls the activation of ER by the posttranslational modification of epigenetic regulators, providing a rationale for epigenetic therapy in ER-positive breast cancer.

Abstract P6-12-01: Phase II study of taselisib (GDC-0032) plus fulvestrant in HER2-negative, hormone receptor-positive advanced breast cancer: Analysis by PIK3CA and ESR1 mutation status from circulating tumor DNA

Background:

The phosphatidylinositol 3-kinase (PI3K) pathway is frequently dysregulated in hormone receptor (HR)-positive breast cancer (BC), with activating mutations of PIK3CA detected in ~35–45% of patients (pts). Acquired mutations in the ESR1 gene, which encodes estrogen receptor α, may be associated with resistance to aromatase inhibitor (AI) therapy. Taselisib is a potent and selective PI3K inhibitor, with greater selectivity against mutant PI3Kα isoforms than wild-type (WT) via a unique mechanism. In phase I studies, taselisib plus fulvestrant had clinical activity and manageable tolerability in pts with HR-positive BC. We report exploratory analyses of PIK3CA and ESR1 from circulating tumor DNA (ctDNA).

Methods:

In this phase II, open-label, single-arm study (PMT4979g; NCT01296555), pts were postmenopausal with HER2-negative, HR-positive locally advanced or metastatic BC and progression or non-response to ≥1 prior endocrine therapy in the adjuvant or metastatic setting. Pts received taselisib (6 mg capsule orally, daily) plus fulvestrant (500 mg intramuscular on Days 1 and 15 of Cycle 1, then Day 1 of each 28-day cycle) until disease progression or unacceptable toxicity. PIK3CA-mutation testing on archival tumor tissue used the cobas® PIK3CA Mutation Test. The Sysmex Inostics' BEAMing Digital PCR platform was used for ctDNA analysis of ESR1 and PIK3CA mutations (pre-dose on Cycle 1, Day 1). Primary endpoints were objective response rate (ORR) and clinical benefit rate (CBR) in all pts and those with PIK3CA mutations. ORR was confirmed complete response (cCR) and confirmed partial response (cPR). CBR was cCR, cPR, or stable disease for ≥6 months. Secondary endpoints included safety, efficacy, pharmacokinetics, and exploratory biomarker analysis.

Results:

60 pts were enrolled. Median age was 61.5 years (range 31–82). In the metastatic setting, pts had received prior chemotherapy (21.7%) and prior hormonal therapy (50.0%). 86.7% of pts had received prior treatment with an AI. 45 pts had PIK3CA mutation status from archival tumor tissue and ctDNA testing; concordance was 86.7% (39/45). ctDNA analysis, vs archival tumor tissue testing, identified 4 pts and 9 pts with PIK3CA mutations from pts with WT and unknown PIK3CA mutation status, respectively.

Based on ctDNA analysis (N=60), 13 pts (21.7%) had mutations in both ESR1 and PIK3CA, 21 pts (35.0%) were 'mutation not detected' (MND) for both genes, 8 (13.3%) had ESR1 mutations and PIK3CA MND, and 18 (30.0%) had ESR1 MND and PIK3CA mutations.

In pts with measurable disease at baseline, confirmed responses (all partial) were: PIK3CA mutation, 38.1% (8/21); PIK3CA MND, 8.7% (2/23); all pts, 22.7% (10/44). CBRs were: PIK3CA mutation, 42.9%; PIK3CA MND, 17.4%; all pts, 29.5%. ORR and CBR from ctDNA analyses were similar to archival tumor tissue data.

Conclusions:

ctDNA analysis identified PIK3CA mutations in pts with previously unknown or WT mutation status from archival tumor tissue; ORR and CBR were similar to those from archival tumor tissue suggesting that PIK3CA mutation testing from ctDNA may be used as a surrogate when tissue is unavailable. 21.7% of pts had mutations in both ESR1 and PIK3CA.

Citation Format: Dickler MN, Saura C, Oliveira M, Richards DA, Krop IE, Cervantes A, Stout TJ, Jin H, Savage HM, Wilson TR, Baselga J. Phase II study of taselisib (GDC-0032) plus fulvestrant in HER2-negative, hormone receptor-positive advanced breast cancer: Analysis by PIK3CA and ESR1 mutation status from circulating tumor DNA [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 P6-12-01.

Abstract P4-21-34: Phase II study of gemcitabine, trastuzumab, and pertuzumab for HER2-Positive metastatic breast cancer after prior pertuzumab-based therapy

Background: The combination of taxanes with trastuzumab (H) and pertuzumab (P) for first line treatment of HER2-positive metastatic breast cancer (MBC) is associated with improved progression-free survival (PFS) and overall survival (OS). Treatment per physician's choice with anti-HER2 therapy after second line therapy is associated with a median PFS of 3 months. While continued use of H in therapeutic combinations after progression on H-based therapy is common, the efficacy of continuing HP-based treatment after progression on P-based therapy is unknown.

Methods: This is a single arm phase II trial of gemcitabine (G) with HP. Eligible patients had HER2-positive (IHC 3+ or FISH ≥ 2.0) MBC with prior HP-based treatment and ≤ 3 prior chemotherapies. Patients received G (1200 mg/m2) on days 1 and 8 of a q 3 week (w) cycle, and H (8 mg/kg load → 6 mg/kg) and P (840 mg load → 420 mg) q3w. The primary endpoint is PFS at 3 months. Secondary endpoints include OS, safety and tolerability. An exploratory endpoint is to compare PFS by RECIST criteria versus 18-F FDG-PET response criteria. Using a Simon optimal 2-stage design, 21 patients were enrolled in stage 1. The successful 3-month PFS rate for stage 1 was set at 57% to allow accrual to stage 2 for a total of 45 patients. The study therapy will be considered successful if at least 27/45 (60%) patients are progression free at 3 months.

Results: As of June 9, 2016, 28 patients are enrolled; 21 are evaluable at 3 months and 7 have not had 3-month evaluation. At 3 months, 16/21 (76%) are progression free; 5 patients have progressed. The 3 month-PFS results for evaluable patients will be updated. There are no cardiac or febrile neutropenic events to date. Initially, 5 of 22 (23%) patients required G dose reduction (4 due to grade 3 neutropenia and 1 due to grade 3 vomiting) and the study was amended to lower initial G dose to 1000 mg/m2.

Conclusions: The preliminary 3 month-PFS is 76% (95% CI 55% to 89%) in evaluable patients, and updated data will be presented. These findings suggest clinical benefit when P is continued beyond progression.

Citation Format: Iyengar NM, Smyth L, Lake D, Gucalp A, Singh JC, Traina TA, DeFusco P, Dickler MN, Fornier MN, Goldfarb S, Jhaveri K, Modi S, Troso-Sandoval T, Argolo D, Jack K, Ulaner G, Jochelson M, Baselga J, Norton L, Hudis CA, Dang CT. Phase II study of gemcitabine, trastuzumab, and pertuzumab for HER2-Positive metastatic breast cancer after prior pertuzumab-based therapy [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 P4-21-34.

18F-Fluoroestradiol PET/CT Measurement of Estrogen Receptor Suppression during a Phase I Trial of the Novel Estrogen Receptor-Targeted Therapeutic GDC-0810: Using an Imaging Biomarker to Guide Drug Dosage in Subsequent Trials

Purpose: Evaluate ¹⁸F-fluoroestradiol (FES) PET/CT as a biomarker of estrogen receptor (ER) occupancy and/or downregulation during phase I dose escalation of the novel ER targeting therapeutic GDC-0810 and help select drug dosage for subsequent clinical trials.Experimental Design: In a phase I clinical trial of GDC-0810, patients with ER-positive metastatic breast cancer underwent FES PET/CT before beginning therapy and at cycle 2, day 3 of GDC-0810 therapy. Up to five target lesions were selected per patient, and FES standardized uptake value (SUV) corrected for background was recorded for each lesion pretherapy and on-therapy. Complete ER downregulation was defined as ≥90% decrease in FES SUV. The effect of prior tamoxifen and fulvestrant therapy on FES SUV was assessed.Results: Of 30 patients who underwent paired FES-PET scans, 24 (80%) achieved ≥90% decrease in FES avidity, including 1 of 3 patients receiving 200 mg/day, 2 of 4 patients receiving 400 mg/day, 14 of 16 patients receiving 600 mg/day, and 7 of 7 patients receiving 800 mg/day. Withdrawal of tamoxifen 2 months prior to FES PET/CT and withdrawal of fulvestrant 6 months prior to FES PET/CT both appeared sufficient to prevent effects on FES SUV. A dosage of 600 mg GDC-0810 per day was selected for phase II in part due to decreases in FES SUV achieved in phase I.Conclusions: FES PET/CT was a useful biomarker of ER occupancy and/or downregulation in a phase I dose escalation trial of GDC-0810 and helped select the dosage of the ER antagonist/degrader for phase II trials. Clin Cancer Res; 23(12); 3053-60. ©2016 AACR.

Breast carcinoma with an Oncotype Dx recurrence score <18: Rate of distant metastases in a large series with clinical follow-up

BACKGROUND

A 21-gene expression assay (Oncotype DX recurrence score [RS]) that uses reverse transcriptase-polymerase chain reaction is used clinically in patients with early-stage, estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast carcinoma (ER+/HER2- BC) to determine both prognosis with tamoxifen therapy and the usefulness of adding adjuvant chemotherapy. Use of the assay is associated with reductions in overall chemotherapy use. The current study examined the treatments and outcomes in patients with low RS.

METHODS

The authors reviewed the institutional database to identify patients with lymph node-negative, ER+/HER2- BC who were treated at the study institution between September 2008 and August 2013 and their 21-gene RS results.

RESULTS

A total of 1406 consecutive patients with lymph node-negative ER+/HER2- BC and a low RS were identified (510 patients had an RS of 0-10 and 896 patients had an RS of 11-17). The median age at the time of diagnosis of BC was 56 years; 63 patients (4%) were aged <40 years. Overall, 1361 patients (97%) received endocrine therapy and 170 patients (12%) received chemotherapy. The median follow-up was 46 months. Six patients (0.4%) developed distant metastases (1 patient with an RS of 5 and 5 patients with an RS of 11-17). In the cohorts of patients with an RS of 11 to 17, the absolute rate of distant metastasis among patients aged <40 years was 7.1% (3 of 42 patients) versus 0.2% among patients aged ≥40 years (2 of 854 patients).

CONCLUSIONS

The data from the current study document a 0.4% rate of distant metastasis within 5 years of BC diagnosis among patients with lymph node-negative ER+/HER2- BC with an RS <18. Patients aged <40 years at the time of BC diagnosis were observed to have a higher rate of distant metastases. Analysis of data from other studies is necessary to validate this observation further. Cancer 2017;131-137. © 2016 American Cancer Society.

Endocrine resistance in hormone-responsive breast cancer: mechanisms and therapeutic strategies

The majority of breast cancers may be considered hormone responsive due to expression of hormone receptors (HR+). Although endocrine therapy is always considered for advanced HR+ breast cancer, the emergence of resistance is inevitable over time and is present from the start in a proportion of patients. In this review, we explore the mechanisms underlying de novo and acquired resistance to endocrine therapy. We comprehensively review newly approved and emerging therapies that have been developed to counteract specific mechanisms of resistance. We discuss the challenges pertinent to this therapeutic arena including the potential relief of negative regulatory feedback inhibition with compensatory pathway activation and the evolution of molecular changes in HR+ breast cancers during treatment. We discuss strategies to address these challenges in order to develop rational therapy approaches for patients with advanced HR+ breast cancer.

Abstract 4509: Clinical genomic profiling of 1000 metastatic breast cancer patients: actionable targets, novel alterations, and clinical correlations

Most large genomic profiling efforts in breast cancer have focused on primary breast tumors. Profiling of metastatic breast cancer (MBC) could more accurately define actionable genomic alterations and reveal novel alterations that arise under the selective pressure and clonal evolution of prior therapy. Utilizing a 410-gene targeted capture-based sequencing platform (MSK-IMPACT), we analyzed 920 tumors (62% metastatic, 38% primary) from 874 MBC patients for somatic mutations, DNA copy number alterations, and structural rearrangements (planned final analysis 1000 patients). Detailed clinical data including treatment outcomes was collected for all patients. The cohort was representative of the well characterized clinical subtypes of breast cancer with 71% ER+ or PR+ and HER2-, 17% HER2+, and 12% triple negative breast cancer (TNBC).

Our analysis revealed recurrent alterations in multiple pathways including PI3K/AKT/mTOR (56%), cell cycle regulation (42%), RTK signaling (40%), epigenetic regulation (33%) and MAPK/ERK (19%) pathways. The most frequent actionable alterations include: PIK3CA mutation (36%), ERBB2 amplification (15%), FGFR1 amplification (12%), ESR1 mutation (11%), PTEN mutation/deletion (10%), AKT1 mutation (6%), and ERBB2 mutation (5%). The genomic landscape was significantly different across breast cancer subtypes. For example, the PI3K/AKT/mTOR pathway was altered in ER+ MBC mainly through activating PIK3CA mutations whereas PTEN deletion/mutations were most common in TNBC. We also identified significant differences in the genomic profiles of metastatic and primary tumor samples. Gene enrichment analyses revealed a subset of genes more frequently altered in metastatic tumors (STK11: 13 vs 2; ROS1: 14 vs 2; FGFR4: 15 vs 1) suggesting that mutations in these genes may play a role in breast tumor metastasis and/or therapy resistance. ESR1 mutations were predominantly present in metastatic tumors (88%) and were significantly associated with duration of prior hormonal therapy (P&lt;0.0001). ESR1 mutations were also associated with a poor response to the ER degrader fulvestrant (median PFS: 4.8 vs 13.7 months, mutated vs wild type; P = 0.01). Analysis for potentially novel hotspot mutations revealed recurrent RHOA G17 mutations in 6 MBC patients, nominating RHOA, a GTPase transducer of membrane receptors, as a candidate driver in a subset of breast cancers. While identified previously in other tumors, RHOA G17 has never been implicated in breast cancer.

In summary, our genomic analyses of this large cohort of MBC patients revealed actionable alterations in over 60% of the patients. 29% of patients with these alterations were enrolled in clinical trials of matched targeted therapies to date (PIK3CA 27%, AKT1 30%, ESR1 23%, ERBB2 39%) suggesting that prospective genomic characterization can accelerate enrollment of patients with MBC onto therapeutic clinical trials.

Citation Format: Pedram Razavi, Matthew T. Chang, Sumit Middha, Dara S. Ross, Ahmet Zehir, Tracy A. Proverbs-Singh, Cyriac Kandoth, Sarat Chandarlapaty, Maura N. Dickler, Jorge S. Reis-Filho, Sujata Patil, Venkatraman Seshan, Lillian Smyth, Neil M. Iyengar, Komal Jhaveri, Shanu Modi, Chau T. Dang, Mark E. Robson, Larry Norton, Clifford A. Hudis, Marc Ladanyi, Maurizio Scaltriti, Nikolaus Schultz, David Hyman, Michael F. Berger, Barry S. Taylor, David B. Solit, José Baselga. Clinical genomic profiling of 1000 metastatic breast cancer patients: actionable targets, novel alterations, and clinical correlations. [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 4509.

Endocrine Therapy for Hormone Receptor-Positive Metastatic Breast Cancer: American Society of Clinical Oncology Guideline

PURPOSE

To develop recommendations about endocrine therapy for women with hormone receptor (HR) -positive metastatic breast cancer (MBC).

METHODS

The American Society of Clinical Oncology convened an Expert Panel to conduct a systematic review of evidence from 2008 through 2015 to create recommendations informed by that evidence. Outcomes of interest included sequencing of hormonal agents, hormonal agents compared with chemotherapy, targeted biologic therapy, and treatment of premenopausal women. This guideline puts forth recommendations for endocrine therapy as treatment for women with HR-positive MBC.

RECOMMENDATIONS

Sequential hormone therapy is the preferential treatment for most women with HR-positive MBC. Except in cases of immediately life-threatening disease, hormone therapy, alone or in combination, should be used as initial treatment. Patients whose tumors express any level of hormone receptors should be offered hormone therapy. Treatment recommendations should be based on type of adjuvant treatment, disease-free interval, and organ function. Tumor markers should not be the sole criteria for determining tumor progression; use of additional biomarkers remains experimental. Assessment of menopausal status is critical; ovarian suppression or ablation should be included in premenopausal women. For postmenopausal women, aromatase inhibitors (AIs) are the preferred first-line endocrine therapy, with or without the cyclin-dependent kinase inhibitor palbociclib. As second-line therapy, fulvestrant should be administered at 500 mg with a loading schedule and may be administered with palbociclib. The mammalian target of rapamycin inhibitor everolimus may be administered with exemestane to postmenopausal women with MBC whose disease progresses while receiving nonsteroidal AIs. Among patients with HR-positive, human epidermal growth factor receptor 2-positive MBC, human epidermal growth factor receptor 2-targeted therapy plus an AI can be effective for those who are not chemotherapy candidates.

Phase III Trial Evaluating Letrozole As First-Line Endocrine Therapy With or Without Bevacizumab for the Treatment of Postmenopausal Women With Hormone Receptor-Positive Advanced-Stage Breast Cancer: CALGB 40503 (Alliance)

PURPOSE

To investigate whether anti-vascular endothelial growth factor therapy with bevacizumab prolongs progression-free survival (PFS) when added to first-line letrozole as treatment of hormone receptor-positive metastatic breast cancer (MBC).

PATIENTS AND METHODS

Women with hormone receptor-positive MBC were randomly assigned 1:1 in a multicenter, open-label, phase III trial of letrozole (2.5 mg orally per day) with or without bevacizumab (15 mg/kg intravenously once every 3 weeks) within strata defined by measurable disease and disease-free interval. This trial had 90% power to detect a 50% improvement in median PFS from 6 to 9 months. Using a one-sided α = .025, a target sample size of 352 patients was planned.

RESULTS

From May 2008 to November 2011, 350 women were recruited; 343 received treatment and were observed for efficacy and safety. Median age was 58 years (range, 25 to 87 years). Sixty-two percent had measurable disease, and 45% had de novo MBC. At a median follow-up of 39 months, the addition of bevacizumab resulted in a significant reduction in the hazard of progression (hazard ratio, 0.75; 95% CI, 0.59 to 0.96; P = .016) and a prolongation in median PFS from 15.6 months with letrozole to 20.2 months with letrozole plus bevacizumab. There was no significant difference in overall survival (hazard ratio, 0.87; 95% CI, 0.65 to 1.18; P = .188), with median overall survival of 43.9 months with letrozole versus 47.2 months with letrozole plus bevacizumab. The largest increases in incidence of grade 3 to 4 treatment-related toxicities with the addition of bevacizumab were hypertension (24% v 2%) and proteinuria (11% v 0%).

CONCLUSION

The addition of bevacizumab to letrozole improved PFS in hormone receptor-positive MBC, but this benefit was associated with a markedly increased risk of grade 3 to 4 toxicities. Research on predictive markers will be required to clarify the role of bevacizumab in this setting.

Cancer and Fertility Program Improves Patient Satisfaction With Information Received

PURPOSE

A cancer and fertility program was established at a large cancer center to support clinicians in discussing treatment-related fertility risks and fertility preservation (FP) options with patients and in referring patients to reproductive specialists. The program provides resources, clinician education, and fertility clinical nurse specialist consultation. This study evaluated the program's impact on patient satisfaction with information received.

PATIENTS AND METHODS

Retrospective cross-sectional surveys assessed satisfaction before (cohort 1 [C1]) and after (cohort 2 [C2]) program initiation. Questionnaires were investigator-designed, gender-specific, and anonymous.

RESULTS

Most C1 (150 males, 271 females) and C2 (120 males, 320 females) respondents were 2 years postdiagnosis; the most frequently reported cancers were testicular, breast, and lymphoma. A significant difference in satisfaction with the amount of information received was seen between C1 and C2. For males, satisfaction with information on fertility risks was high in both cohorts but significantly greater in C2 for information on sperm banking (χ(2) = 9.3, P = .01) and finding a sperm bank (χ(2) = 13.3, P = .001). For females, satisfaction with information was significantly greater in C2 for information on fertility risks (χ(2) = 62.1, P < .001), FP options (χ(2) = 71.9, P < .001), help with decision making (χ(2) = 80.2, P < .001), and finding a reproductive endocrinologist (χ(2) = 60.5, P < .001). Among patients who received and read information materials, 96% of males and 99% of females found them helpful. Among C2 females, fertility clinical nurse specialist consultation was associated with significantly greater satisfaction with information on FP options (χ(2) = 11.2, P = .004), help with decision making (χ(2) = 10.4, P = .006), and finding a reproductive endocrinologist (χ(2) = 22.6, P < .001), with 10% reporting lack of knowledge as a reason for not pursuing FP.

CONCLUSION

Improvements in patient satisfaction with information received demonstrate the potential for fertility programs in cancer care settings to improve the quality of clinician-patient discussions about fertility.

Molecular Imaging of Biomarkers in Breast Cancer

The success of breast cancer therapy is ultimately defined by clinical endpoints such as survival. It is valuable to have biomarkers that can predict the most efficacious therapies or measure response to therapy early in the course of treatment. Molecular imaging has a promising role in complementing and overcoming some of the limitations of traditional biomarkers by providing the ability to perform noninvasive, repeatable whole-body assessments. The potential advantages of imaging biomarkers are obvious and initial clinical studies have been promising, but proof of clinical utility still requires prospective multicenter clinical trials.

Is There a Role for Oncotype Dx Testing in Invasive Lobular Carcinoma?

Oncotype Dx Breast Cancer Assay is a 21-gene assay used in estrogen receptor (ER)-positive breast cancer to predict benefit from chemotherapy (CT). Tumors are placed into one of three risk categories based on their recurrence score (RS). This paper explores the impact of tumor histopathologic features and Oncotype Dx RS on the treatment plan for invasive lobular carcinoma (ILC). Invasive lobular carcinoma cases submitted for Oncotype Dx testing were identified from a clinical data base. The histopathologic and immunohistochemical features and RS subcategory of each tumor, and treatment regimen and medical oncologic assessments of each patient were reviewed. A total of 135 cases of ILC had RS testing, which represented 15% of all ILC diagnosed at the institution over the time period. 80% of ILC was of the classical subtype and all tumors were ER positive and human epidermal growth factor receptor 2 (HER-2) negative by immunohistochemistry. Sixty three percent of cases were low risk (LR), 35.5% were intermediate risk (IR) and 1.5% were high risk (HR). Both HR cases were pleomorphic ILC. Sixty eight percent of classical ILC had a LR score, while 70% of pleomorphic ILC had an IR score. Patients in the IR category were significantly more likely to undergo CT than patients in the LR category (54% versus 18%; p < 0.0001). In the LR category, those undergoing CT were significantly younger and more likely to have positive lymph nodes (p < 0.05). Qualitative analysis of medical oncologic assessments showed that RS played a role in decision-making on CT in 74% of cases overall. At our institution, Oncotype Dx RS currently plays a role in the management of a proportion of ILC and impacts on treatment decisions.