1st Line Endocrine Therapy Research Articles

Serial analysis of ESR1 and PIK3CA mutations in cell-free DNA from metastatic breast cancer during 1st line endocrine therapy.

e13060 Background: Activating mutations ofESR1 and PIK3CA genes are known mechanisms of endocrine resistance. Recent analysis supported benefit of early intervention at presence of ESR1 mutation in blood (bESR1) before clinical progression. We aimed to investigate ESR1 and PIK3CA mutations detected in cell-free DNA (cfDNA) from patients with hormone receptor-positive, HER2-negative metastatic breast cancer (MBC) and its impact on progression-free survival (PFS). Methods: Thirty patients undergoing 1st line endocrine therapy (ETx) were identified from a prospective cohort. Seven ESR1 hotspot mutations in the ligand binding domain were tested in cfDNA with droplet digital polymerase chain reaction (ddPCR) assay (Genopeaks Co., Ltd). Eleven PIK3CA hotspot mutations were tested using amplicon-targeted sequencing method (Genopeaks Co., Ltd) in both tumor and cfDNA. PFS analyses were performed using Kaplan-Meier methods and compared with the log-rank test. Results: We examined serial cfDNA samples from 26 patients collected every 3-6 months. ESR1 mutations were found in 61.5% (16/26) patients at any timepoint during 1st line endocrine therapy, with D538G being the most common followed by Y537C and 68.8% (11/16) being polyclonal. Among the 50.0% (8/16) bESR1 positive patients with clinical progression, 4 had bESR1 detected before clinical progression while 4 were diagnosed clinical progression concurrently, suggesting the necessity of closer intervals of cfDNA analyses. While presence of bESR1 did not affect PFS overall, 18.8% of patients with bESR1 detected within 6 months after 1st line ETx, displayed worse outcome (median PFS 5 vs 52 months). Also, patients with clearance of bESR1 mutation in subsequent cfDNA (81.3%, 13/16) were shown to have a better outcome (median PFS 52 vs 41 months). Among 14 patients with clinical progression, 8 had bESR1 mutation. Median PFS between patients with bESR1 positive vs negative was 14 vs 9 months. PIK3CA mutations were detected in 69.5% (16/23) of cfDNA at diagnosis of distant metastasis, among them 53.3% (8/15) had co-occurrence with bESR1 mutations. While presence of PIK3CA mutation in primary tumor tissue did not affect disease-free survival nor PFS, patients with blood PIK3CA mutation at diagnosis of metastasis displayed significantly worse outcome (p = 0.041). Conclusions: Substantial number of hormone receptor-positive, HER2-negative MBC patients were detected with ESR1 and PIK3CA mutation in plasma. Though it was a small-sized analysis to accurately assess statistical significance, we observed worse outcome in patients with 1) early detection (<6 months) of bESR1 and with 2) sustained bESR1 during palliative ETx. Patients with clinical progression without bESR1 mutation displayed shorter PFS than patients with bESR1. PIK3CA mutations in cfDNA were prognostic supporting the benefit of combined targeted therapy.

Palbociclib (P) plus tamoxifen (TAM) ± goserelin in women with hormone receptor-positive (HR+)/HER2-negative (HER2−) advanced breast cancer (ABC): Primary results of NCCH1607/PATHWAY, an Asian international double-blind randomized phase 3 trial.

LBA1068 Background: In Asian countries, BC incidence rates are rising, with a higher proportion of pre/perimenopausal (pre/peri-M) patients (pts). Data on treatment options for pre/peri-M pts are limited. Adding P to endocrine therapy (ET), such as aromatase inhibitor or fulvestrant, has improved progression-free survival (PFS) in phase 3 studies. However, the efficacy and safety of P in combination with TAM are still unclear in pts with HR+/HER2− ABC regardless of M status. This combination was investigated in PATHWAY (NCT03423199): a double-blind randomized phase 3 trial conducted in Japan, Korea, Taiwan and Singapore. The study was conducted as a Clinical Research Collaboration with the National Cancer Center Hospital being the regulatory sponsor and Pfizer providing drug and financial support. Methods: Women with HR+/HER2− ABC were randomly assigned 1:1 to receive either P (125 mg once daily, days 1-21 of a 28-day cycle) or placebo in combination with TAM (20 mg once daily, continuously) as 1st or 2nd line treatment for ABC. Pre/peri-M women received concurrent ovarian function suppression with goserelin. Pts were stratified by 1st vs 2nd line ET and M status. The primary endpoint was PFS as assessed by investigators. Secondary endpoints include overall survival (OS), objective response, safety, and patient-reported outcomes. Results: A total of 184 pts were assigned to P + TAM (91 pts) and placebo + TAM (93 pts). At data cutoff date (Sep 15, 2022), 138 PFS events had occurred. Median follow-up was 40.9 months for censored pts. Median PFS was 24.4 months (95% CI: 13.1, 32.4) with P + TAM and 11.1 months (95% CI: 7.4, 14.6) with placebo + TAM (hazard ratio [HR]: 0.602 [95% CI: 0.428, 0.848], 1-sided p-value from stratified log rank test: 0.002). The HRs for PFS of the subgroups by stratification factors were as follows: for pts with 1st line ET (HR: 0.521 [95% CI: 0.332, 0.817]) or with 2nd line ET (HR: 0.707 [95% CI: 0.421, 1.189]), and for pre/peri-M pts (HR: 0.378 [95% CI: 0.192, 0.742]) or post-M pts (HR: 0.677 [95% CI: 0.456, 1.005]). While OS data were still immature, the primary analysis showed a 27% reduction in overall risk of death (median OS: not reached in both arms, HR: 0.73 [95% CI: 0.442, 1.207]). 93.4% of pts with P + TAM vs. 20.4% of pts with placebo + TAM had grade (G) ≥3 treatment-emergent adverse events (TEAEs). The most frequently observed G ≥3 TEAE was neutropenia (89.0% in P + TAM arm and 1.1% in placebo + TAM arm). There were no G5 TEAEs in either arm. Conclusions: The study achieved its primary endpoint, demonstrating a significant and clinically meaningful improvement in PFS for P + TAM compared with placebo + TAM for pts with HR+/HER2− ABC. Early OS data with P+TAM is encouraging. TEAEs were generally consistent with the known safety profile of P and ET. Clinical trial information: NCT03423199 .

The prognostic value of chemotherapy or endocrine therapy choice according to circulating tumor cell count in HR+HER2- metastatic breast cancer: a retrospective study.

BackgroundCirculating tumor cell (CTC) count have prognostic role for metastatic breast cancer (MBC). No clear biomarkers can guide selection of chemotherapy (CT) or endocrine therapy (ET) in 1st-line setting of hormone-receptor positive and human epidermal growth factor receptor 2 negative (HR+HER2−) MBC. The present study investigated the prognostic role CT or ET according to the CTC count in HR+HER2− MBC.MethodsWe consecutively collected the data of 53 HR+HER2− MBC patients who received 1st-line CT or ET, who had CTC count detected by our peptide-based nanomagnetic CTC isolation system (Pep@MNPs) from January 2014 to December 2015. The clinicopathological characteristics according the CTC count and 1st-line ET vs. CT were compared. Follow-up was conducted every 6 months. The primary endpoint was progression-free survival (PFS) and overall survival (OS). A Cox regression analysis was conducted to determine the prognostic roles of CTC and 1st-line therapy of ET vs. CT for PFS and OS.ResultsThe median CTC count of the 53 patients was 2 (range, 0–18). The clinicopathological characteristics of the patients in the CTC count <2 group and the CTC count ≥2 group were similar. The patients with a CTC count <2 had a significantly longer PFS than those with a CTC count ≥2 (P=0.005, hazard ratio =4.138, 12.1 vs. 7.1 months). The patients who received CT had a significantly longer PFS than those who received ET (P=0.041, hazard ratio =2.721, 9.9 vs. 7.2 months). In the CTC count ≥2 group, the patients who received CT had a significantly longer PFS than those who received ET (P=0.048, hazard ratio =2.475, 8.7 vs. 6.3 months). In the CTC count <2 group, there was no significant difference in PFS between the CT and ET groups (P=0.071). Additionally, the CTC count had no significant effect on OS (P=0.116, hazard ratio =2.391, 54.2 vs. 34.2 months).ConclusionsThe present study showed that CTC count determined by the Pep@MNP system confirmed the prognostic value in the HR+HER2− MBC patients. And it might be helpful in choosing a 1st-line treatment of CT or ET for HR+HER2− MBC patients.

Abstract CT028: A pilot study of pembrolizumab and exemestane/leuprolide in premenopausal hormone receptor positive/HER2 negative locally advanced or metastatic breast cancer (PEER)

Abstract Interim Analysis Background: Despite the success of immunotherapy in triple negative breast cancer, no approved immunotherapy is available for HR+, HER2- MBC patients. Among HR+/HER2- patients(pts), luminal subtype B pts who are more resistant to endocrine therapy, demonstrate higher tumor infiltrating lymphocytes, higher immune score, and higher expression of PD-L1 than luminal subtype A pts. In addition, estrogen is known to result in immunosuppressive microenvironment. Exemestane, as a steroidal aromatase inhibitor, provides less than 10% overall response rate in second or third line of endocrine therapy for MBC pts. This pilot study aims to observe the efficacy of a combination of exemestane, leuprolide, and pembrolizumab in pre-/perimenopausal HR+, HER2- locally advanced or MBC pts who failed front-line endocrine therapy. Methods: This single-center, nonrandomized, open-label, phase Ib/II study of exemestane/leuprolide plus pembrolizumab enrolled a cohort of endocrine resistant HR+, HER2-, pre-/perimenopausal, locally advanced or MBC pts who 1) had failed adjuvant endocrine therapy within 12 months, 2) had failed at least 2 lines of prior endocrine therapy for MBC, 3) had failed 1st line endocrine therapy within 6 months or 1st line endocrine therapy+ CDK4, 6 inhibitor within 12 months. No prior chemotherapy for locally advanced or MBC was allowed. Patients received 25mg exemestane orally daily, 3.6mg leuprolide subcutaneous injection every 28 days, and pembrolizumab 150mg IV on day 1/day 15 every 28 days. Primary objective was to estimate the efficacy of the exemestane, leuprolide plus pembrolizumab combination defined by progression-free survival (PFS) rate at 8 months. Secondary objectives included safety, objective response rate (ORR), clinical benefit rate (CBR), and PFS. Results: Of 14 pts enrolled, 6 (42.9%) received 1 line and 8 (57.1%) received 2 lines of prior endocrine therapy in the locally advanced/metastatic setting. Safety of the combination was generally consistent with known side effects of exemestane, leuprolide, and pembrolizumab and was generally manageable. Grade 3/4 adverse events in ≥1 pt included AST increase (4 pts/28.6%), ALT increase (4 pts/28.6), and hypo/hyperthyroidism (1 pt, 7.1%). Nine pts did not progress or die at 8 months (64.3% PFS rate at 8th month). In the 13 evaluable pts, 5 had confirmed partial response [PR] (ORR=38.4%), 6 had confirmed stable disease[SD, 46.2%]. The disease control rate (complete response [CR]+partial response [PR]+stable disease [SD]) was 84.6%. CBR (CR+PR+SD persisting for ≥6 months) was 76.9%. Median PFS of the evaluable pts, PR pts, SD pts, and PD pts were 10.2 months, 15.8months, 10.1 months, and 2.4 months respectively. Conclusions: Combination of exemestane, leuprolide plus pembrolizumab demonstrated a generally tolerable safety profile with numerically higher rate of transaminase elevations than reported for the individual treatments. Compared to historical data for exemestane/leuprolide or for pembrolizumab monotherapy in a similar pt population, a meaningful higher ORR and longer PFS were observed. Citation Format: I-Chun Chen, Ching-Hung Lin, Dwan-Ying Chang, Tom Wei-Wu Chen, Ming-Yang Wang, Wei-Li Ma, Yi-Ting Lin, Shu-Min Huang, Yen-Shen Lu. A pilot study of pembrolizumab and exemestane/leuprolide in premenopausal hormone receptor positive/HER2 negative locally advanced or metastatic breast cancer (PEER) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT028.

Abstract P2-11-06: Assessment of ESR1 genomic aberrations and their role in endocrine therapy resistance in breast cancer

Abstract Background: Endocrine therapy (ET) is an effective treatment of estrogen receptor positive (ER+) breast cancer (BC). However, not all ER+ cancers respond to ET and many eventually acquire resistance. Genomic aberrations in ESR1 have been reported to play a role in resistance to treatment. ESR1 mutations (ESRMs), reported in 10-50% of metastatic or recurrent BCs treated with aromatase inhibitors (AIs), can lead to constitutive activation and reduced sensitivity to ET. The incidence and clinical implications of ESR1 amplification (ESRA) is not well-established. A variety of structural rearrangements involving ESR1 have been reported in primary BCs, with some more strongly associated with tamoxifen and AI resistance. This study aimed to establish a rapid, reliable and cost-effective method to screen and monitor ESR1 genomic aberrations in clinical BC tissue samples and relate these to the 1st line and subsequent ETs patients received. Patients: • Cohort A - 20 post-menopausal women (PMW) with ER+ BC who had acquired resistance to AIs and received subsequent lines of ET. Previous NGS data were available for these patients. • Cohort (B) - 425 ER+ BC patients, with paired matched tissue samples from the primary and progressive/recurrent cancer on 1st line ET; sites included local recurrence (25%), nodal recurrence (29%), distant recurrence (3%) and primary progression on neoadjuvant ET (44%). Median follow-up 10 years. All patients received 2nd line ET, 14% developed a further recurrence on 2nd line ET. Methods: ESRMs were assessed by allele-specific real-time quantitative (rt-qPCR) and digital droplet PCR (ddPCR) assays, a novel fluorometric in situ mutation detection (ISMD) approaches and AmpliSeq targeted sequencing. ESRA and ESR1 fusions were detected by targeted sequencing and validated using FISH and custom ligation assays for commonly-reported fusion proteins (currently ESR1-e6&amp;gt;YAP1 and ESR1-e6&amp;gt;PCDH11X), respectively. Results: Results from ddPCR and ISMD were consistent with NGS findings in cohort A. There was expansion of D538G mutant clones with acquired resistance in 5/20 patients (25%). ESR1 copy number gain was seen in 11/20 patients (55%) in resistant samples. Gene amplification was confirmed by FISH in 6, corresponding to those with the highest gain from the NGS data. In cohort B, recurrent/resistant samples (including 2nd recurrences) with matched primaries are currently being screened for ESR1 genomic aberrations using all methods allowing for a comprehensive comparison. This will allow full characterisation of mutations, copy number changes and gene fusions in the largest cohort of ET resistant cancers to date. Results will be interpreted in the context of 1st line ET (51% Tamoxifen, 34% non-steroidal AI, 8% exemestane, 7% other ET) and 2nd line ET in the 14% of patients who developed a 2nd recurrence. ESR1 genomic aberrations have been identified in 38% of samples to date, with specific aberrations associated with particular ETs. Discussion: • A reliable, robust and cost-effective methodology for the detection and quantitation of ESR1 aberrations in clinical BC samples has been developed and compared with NGS and targeted sequencing approaches. • This method would allow rapid screening for key aberrations with the potential to inform selection of 2nd line therapy. • Multiplexing of fluorometric assays may enable in situ clonality analysis that allows visualisation of multiple genomic driver aberrations simultaneously. • In the largest cohort of patients with resistance to ET to date, there is a high incidence of ESR1 genomic aberrations. These are associated with specific ETs. Analysis between these changes and response, disease-free and overall breast cancer-specific survival on 2nd line ET is currently ongoing. Citation Format: Carlos Martinez-Perez, Charlene Kay, James Meehan, Mark Gray, Rebecca Swan, Lorna Renshaw, Jane Keys, Andrew H Sims, Olga Oikonomidou, J Michael Dixon, Arran K Turnbull. Assessment of ESR1 genomic aberrations and their role in endocrine therapy resistance 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 P2-11-06.

Abstract P6-04-03: In-depth genomic analysis of acquired resistance to multiple sequential lines of endocrine therapy in breast cancer

Abstract Background: 80% of all breast cancers (BCs) are ER+. Not all respond to endocrine therapy (ET) and many eventually develop resistance. An in-depth genomic analysis of cancers that acquired resistance (aR) to multiple sequential lines of ET after an initial period of response has been performed. Patients: A unique cohort of tissues from 20 post-menopausal women with ER+ BC was collected. All patients initially responded to neoadjuvant ET; 19/20 received an aromatase inhibitor (AI): letrozole (LET) (n=18) or anastrozole (AN) (n=1), 1 patient received fulvestrant followed by adjuvant tamoxifen (TAM) (mean treatment duration 22 months, range 4-67) before developing resistance. Patients were then treated by surgery or 2nd line ET. Overall, 13/20 received 2nd line ET either AN (n=1), TAM (n=10) or exemestane (EX) (n=1); 6 went on to receive 3rd line ET with EX (n=5) or LET (n=1). Methods: Serial RNA &amp; DNA from 3-5 cancer samples per patient (89 samples) had Ribo0-RNAseq and DNA exome sequencing. Somatic mutations and copy number alterations (CNA) were determined. Fisher’s exact test was used to compare mutation frequencies (MFs). Differential gene expression analysis was performed using two-class unpaired Significance Analysis of Microarrays (SAM). Results: Mutations: Comparisons of MFs between all sensitive vs resistant tumours identified mutations in SAAL1 and SLC9A9 as being enriched in sensitive tumours while mutations in GATA3 and ZFPM2 were enriched across tumours with acquired resistance to ET. Only KMT2C was identified as enriched in resistant tumours when comparing sensitive to only those that acquired resistance to 1st line LET. When comparing sensitive tumours to only those that had acquired resistance to multiple lines of ET (LET and TAM +/- AN and EX), sensitives were significantly enriched for mutations in CCDC141 and SLC9A9 and multi-drug resistant (MDR) tumours were significantly enriched for mutations in 11 genes including ESR1 and GATA3, and genes involved in cell adhesion (CDH1, FLG, FLG2 and FREM2). ESR1 mutations were identified in 6/20 patients; 5 patients had D538G mutations, 2 appeared during resistance to 1st line LET and 3 in MDR tumours. 1 patient had an ESR1 frame-shift mutation which appeared during resistance to 1st line LET. GATA3 was mutated in 7/20 patients, of which 4 had mutations in all samples including baseline, 2 had mutations uniquely present in MDR tumours and 1 had mutations that appeared during resistance to 1st line LET. CNA: No significant gains or losses were identified when comparing sensitive tumours to those resistant to 1st line LET alone, but significant gains were identified across multiple chromosomes in MDR tumours. Gain of ESR1 was seen in 8/20 patients; in 3 patients there was ESR1 gain at diagnosis which persisted through initial response and subsequent aR. 5 patients developed ESR1 gain during MDR but not during initial resistant to 1st line LET. Gene Expression: Analysis comparing sensitive and MDR tumours identified 82 differentially expressed genes (FDR=0). MDR tumours had higher proliferation and higher expression of transcriptional regulators including FOS and FOSB, histone cluster genes and genes involved in oxidative phosphorylation. MDR tumours also had higher expressions of GATA3 induced genes. Discussion: In contrast to 1st line ET resistance, aR to multiple lines was characterised by significant gains across multiple chromosomes including ESR1 gain in a quarter of tumours. MDR tumours were also characterised by enrichment of mutations in particular genes including ESR1 (D538G in particular) which occurs in one-third of patients with aR. GATA3 is expressed in &amp;gt;90% of BCs, is reported to be mutated in up to 10% of all BCs may be integral to the functions of ESR1; mutations in GATA3 were enriched in MDR tumours and may highlight a new area of ET resistance. Citation Format: Arran K Turnbull, Youli Xa, Carlos Martinez-Perez, Olga Oikonomidou, James Meehan, Mark Gray, Lisa A Carey, Charles M Perou, J Michael Dixon. In-depth genomic analysis of acquired resistance to multiple sequential lines of endocrine therapy 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 P6-04-03.

Abstract OT3-02-02: PATHWAY: Asian, multicenter, phase 3 trial of tamoxifen with or without palbociclib ± goserelin in women with hormone receptor-positive, HER2-negative advanced or metastatic breast cancer

Abstract BACKGROUND: The incidence rates of breast cancer (BC) in Asian counties have been rising rapidly. The age-specific female BC incidence rates peak before menopause (around 40-50 years of age) in Asia, however treatment options for pre/perimenopausal patients are limited. Palbociclib (P) is an oral novel cyclin-dependent kinase 4/6 (CDK4/6) inhibitor. The addition of P to endocrine therapy (ET) such as aromatase inhibitor or fulvestrant has been demonstrated improved progression-free survival (PFS) in phase 3 studies PALOMA-2 and PALOMA-3. This study is designed to evaluate efficacy and safety of P plus tamoxifen (TAM) in patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced or metastatic BC regardless of menopausal status. This study is conducted as a Clinical Research Collaboration by National Cancer Center Hospital with research funding from Pfizer. TRIAL DESIGN: PATHWAY/NCCH1607 is a double-blind, placebo-controlled, randomized, phase 3 study. Patients will be randomized 1:1 to receive either P (125 mg once daily, days1-21 of a 28-day cycle) or placebo in combination with TAM (20 mg once daily, continuously). Pre/perimenopausal women should receive concurrent ovarian function suppression with goserelin. Randomization will be stratified by prior ET for advanced/metastatic BC (1st line ET vs. 2nd line ET) and menopausal status (pre/perimenopausal vs. postmenopausal). KEY ELIGIBILITY CRITERIA: Eligible patients include women of any menopausal status with HR-positive, HER2-negative advanced or metastatic BC; candidates to receive TAM as 1st line or 2nd line ET for advanced/metastatic disease; ≥18 years of age; measurable or non-measurable disease (RECIST v.1.1); ECOG performance status 0-1; adequate organ function; have not received treatment with TAM (except for patients who have had more than 12 months from completion of adjuvant therapy with TAM); and have not received any CDK4/6 or phosphoinositide 3-kinase (PI3K) - mammalian target of rapamycin (mTOR) inhibitors. SPECIFIC AIMS: The primary endpoint is PFS as assessed by the investigator. Secondary endpoints include overall survival (OS), 1, 2, and 3-year survival probabilities, objective response (OR), duration of response, clinical benefit rate (CBR), pharmacokinetics, safety, and patient-reported outcomes. STATISTICAL METHODS: The sample size was determined to detect a 38% reduction in the hazard of disease progression or death in P plus TAM arm with a 1-sided significance level of 2.5% and power of 80%. A stratified log rank test will be used to compare PFS between the 2 treatment arms. PRESENT ACCRUAL AND TARGET ACCRUAL: Target accrual of 180 patients will be enrolled within 23 sites among Japan, Korea, Taiwan, and Singapore. As of June 2018, 46 patients have been enrolled. CONTACT INFORMATION: This trial is registered at ClinicalTrials.gov NCT03423199 and UMIN000030816. For more information, email NCCH1607_office@ml.res.ncc.go.jp Citation Format: Noguchi E, Hata T, Nakamura K, Kuchiba A, Hayashi M, Hamada A, Yonemori K, Sohn J, Lu Y-S, Yap Y-S, Fujiwara Y, Tamura K. PATHWAY: Asian, multicenter, phase 3 trial of tamoxifen with or without palbociclib ± goserelin in women with hormone receptor-positive, HER2-negative advanced or metastatic breast cancer [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 OT3-02-02.

Abstract P4-13-11: Meta-analyses of visceral versus non-visceral metastases treated by SERM, AI &amp; SERD agents as 1st line endocrine therapy (ET) for HR+ breast cancer (BC)

Abstract Introduction: There is continuing debate whether efficacy of ET is different in non-visceral metastases (nVM) than VM. Recently fulvestrant 500mg, has been reported to have greater efficacy than an aromatase inhibitor (AI), anastrozole, particularly in nVM – implying efficacy may be both site and agent dependent. Absence of significant overall survival (OS) difference in PALOMA 1 &amp; 3 has increased interest in site of disease, especially given the OS advantage for fulvestrant 500mg monotherapy. Patients &amp; Methods: Individual patient level data was obtained from 7 randomised controlled trials (RCTs) involving SERM, AI &amp; SERD used as 1st Line ET in known HR+ BC were used in this meta-analysis (MA). Five were Phase 3 double-blind, placebo controlled RCTs. Details of the studies, type of ET and patient numbers are shown in Table. All were rigorously assessed for clinical benefit rate (CBR), progression free survival (PFS), duration of clinical benefit (DoCB) and OS.: Details of the studies, types of ET and patient numbers are shown in the Table. Aa two stage MA IPD meta-analysis was used to analyse these outcomesCBR, PFS, OS &amp; DoCB. Peto method for pooled odds ratios was used to calculate p values and CI for CBR, yYusef pPeto method was used to calculate p-values and CI for PFS, OS, and DoCB. Random effect for trial was included when Tarone's test for heterogeneity was significant, otherwise fixed effect models were generated. Results: Outcome data is present for each study and then summarised under SERM, AI, SERD and 'all Ets combined'. Odds Ratios (Ors) &amp; Hazard Ratios (HRs) for VM versus nVM by endocrine agent are shown in the Table ETStudyNo. of Pats.HR+ Pats.CBRPFSOSDoCBSERM(n)(n)OR (95%CIs)HR (95%CIs)HR (95%CIs)HR (95%CIs)TamEORTC1891781.410.850.770.95Tam00273281441.330.981.051.26Tam00301821622.800.590.440.79Tam00252742091.100.780.730.78subtotal9736931.53** (1.11-2.10)0.79** (0.67-0.94)0.70* (0.52-0.94)0.92 (0.72-1.18)AIExeEORTC1821680.841.110.731.02Ana00273401543.850.550.361.06Ana00301711510.970.881.140.82AnaFALCON2322321.070.980.831.05AnaFIRST1031030.970.540.510.53Subtotal10288081.28 (0.73-2.22)0.80 (0.60-1.06)0.66* (0.45-0.95)0.92 (0.74-1.14)SERDFul 500CONFIRM1621622.940.630.561.15Ful 500FALCON2302302.710.410.450.61Ful 500FIRST1021024.110.580.440.55Subtotal4944943.06*** (2.00-4.06)0.56*** (0.45-0.70)0.50*** (0.39-0.65)0.71* (0.53-0.91)Total249519981.66*** (1.37-2.02)0.73*** (0.62-0.86)0.61*** (0.53-0.71)0.87* (0.75-1.00)CBR-Clinical Benefit Rate (n)= number of patients, pvalues p&amp;lt;0.05*, p&amp;lt;0.01**, p&amp;lt;0.001*** Conclusions: This is the largest reported individual patient MA for nVM versus VM in patients with known HR+ advanced BC and clinical outcomes (CBR, DoCB, PFS &amp; OS) approved to regulatory standards. 1) nVM had significantly better clinical outcomes compared to VM when treated by anti-estrogen receptor blocking agents (SERM &amp; SERD) but not when treated by Ais, which have a fundamentally different mechanism of action. 2) SERD (Fulvestrant 500mg) significantly increased all four clinical outcomes. For nVM compared to VM, fulvestrant put more patients into CB, kept them in remission (DoCB) for longer, resulting in 44% reduction in disease progression and a 50% reduction in death. 3) Site of metastases (ie nVM or VM) is one of the factors to consider when selecting patients for endocrine mono or combination ET (plus CDK4/6i) in the 1st Line setting. Citation Format: Robertson JFR, Paridaens R, Bogaerts J, Lichfield J, Bradbury I, Campbell C. Meta-analyses of visceral versus non-visceral metastases treated by SERM, AI &amp; SERD agents as 1st line endocrine therapy (ET) for HR+ breast cancer (BC) [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 P4-13-11.

Abstract P5-11-02: Recurrent ESR1 fusions in primary tumors; a promising predictive factor for outcome to first-line endocrine therapy?

Abstract Introduction: While fusion genes have been identified and are being utilized as prognostic and predictive markers in various types of cancer, their relevance still needs to be established and verified for breast cancer. Recently, recurrent estrogen receptor alpha (ESR1) fusion genes have been identified as putative endocrine resistance markers, but their predictive value for response to endocrine therapy has not yet been independently validated. Here we studied the presence of fusions of ESR1 exon 2 with exons 1 to 11 of CCDC170, resulting in constitutively activated CCDC170, of ESR1 exon 4 with AKAP12, a putative tumor-suppressor gene, and ESR1 exon 1 with C6orf211/ARMT1, a methyltransferase and their association with outcome in a large cohort of ESR1-positive metastatic breast cancer patients. Methods: Fusion gene mRNA levels were measured in 307 ESR1-positive primary tumors by quantitative reverse transcriptase PCR (RT-qPCR). If the RT-qPCR generated a positive Cq value, the expected fusion gene product sizes were validated by MultiNA. All patients in this study were hormone-naïve and all experienced a recurrence and subsequently received 1st line endocrine therapy. The association of the presence of ESR1 fusion genes in the primary tumor with disease-free interval (DFI) before, and progression-free survival (PFS) up to 36 months after start with 1st line tamoxifen (n=219) or aromatase inhibitors (n=88), were evaluated. Results: 74 patients (24.1%) experienced a disease recurrence within one year after removal of the primary tumor (mean DFI; 34.8 months) and 257 patients (83.7%) progressed on 1st-line endocrine therapy within 3 years (mean PFS; 12.5 months). For the tamoxifen cohort, ESR1-CCDC170 fusion transcripts were found in 84 patients, of which fusions restricted to exon 1, 4, 6, 10 and 11 of CCDC170 were present in 18 patients who all but one progressed within 3 years (mean PFS 9.1 months). Of note, overall, these 18 patients also had a reduced DFI. Similarly for the 7 patients with ESR1-AKAP12 fusions and the one patient with an ESR1- ARMT fusion; all these patients progressed within 3 years. But in contrast to the ESR1-CCDC170 fusion positive patients, these patients had a prolonged DFI {see Table). Similar observations were made for the smaller AI cohort, though with the - with respect to their predictive value - most relevant ESR1-CCDC170 fusions restricted to exon 4, 5, 6 and 10 of CCDC170 and here we now also observed a decreased DFI for the 7 patients with ESR1-AKAP12 and the 3 patients with ESR1- ARMT1 fusions (see Table). 1st line tamoxifen (n=219)1st line AI (n=88)Fusion% positiveDFI (months) pos/allPFS (months) pos/allFusion% positiveDFI (months) pos/allPFS (months) pos/allE2-CCDC170 Exon 2 to 1/4/6/10/118.2%19.8/27.99.1/12.0E2-CCDC170 Exon 2 to 4/5/6/1012.5%32.4/51.910.5/13.8E2-AKAP123.2%33.1/27.711.9/12.0E2-AKAP128.0%23.6/54.710.3/12.0E2-ARMT10.5%(n=1)(n=1)E2-ARMT13.4%30.3/52.79.3/12.0 Conclusion: Measuring recurrent ESR1 fusions in primary breast cancer might become a promising tool to identify patients with intrinsic resistance to endocrine therapy or aggressive disease biology. Importantly however, which fusions are relevant appears to depend on the type of endocrine therapy given. Citation Format: Sieuwerts AM, Vitale SR, Bos M, Sleijfer S, Martens JW. Recurrent ESR1 fusions in primary tumors; a promising predictive factor for outcome to 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 P5-11-02.

Abstract P5-04-14: Tracking ESR1 mutation clonal evolution in breast cancer using in situ mutation detection

Abstract Background: Approximately 70% of breast cancers (BCs) are estrogen receptor positive (ER+). Not all ER+ cancers respond to endocrine therapy (ET) and many eventually develop acquired resistance. Next-generation sequencing (NGS) has shown ESR1 mutations (ESRMs) are present in 10-50% of recurrent/metastatic cancers treated with aromatase inhibitors (AIs). Many of these mutations are located in the ligand-binding domain of ER, so they can lead to constitutive activation. This suggests ESRMs are a major mechanism of acquired resistance to endocrine therapy (ET) and numerous studies have shown a link between ESRMs and reduced sensitivity to 2nd line ET. The aim of this project was to investigate the incidence and clonal evolution of common ESRMs in BCs resistant to multiple sequential ETs using NGS, as well as novel PCR and in situ mutation detection methods. Methods: We have optimised an allele-specific real-time PCR (rtPCR) assay and an in situ mutation detection method (ER-ISMD) for the assessment of ESRMs. Both have been designed to identify a missense gain-of-function D538G mutation with a single nucleotide-resolution in formalin-fixed paraffin-embedded (FFPE) BC tissues. Two unique cohorts have been studied: (A) 20 post-menopausal women (PMW) with ER+ BC who acquired resistance to letrozole and were treated with up to 4 subsequent lines of ET. Serial RNA and DNA from 3-5 cancer samples per patient (58 samples from 20 patients) were analysed by Ribo0-RNAseq, DNA exome sequencing, rtPCR and ER-ISMD. (B) 150 PMW with ER+ BC who developed local (n=79), lymph node (n=59) or distant (n=12) recurrences on 1st line adjuvant letrozole, anastrozole or tamoxifen. Of these, 48 patients developed subsequent recurrences on 2nd line ET. Tissue samples from each recurrence and matched primary BC were collected. Results: In cohort A, 5/20 patients (20%) had expansion of a D538G ESR1 mutation clone at time of resistance 1st line ET (3:letrozole, 1:anastrozole, 1:tamoxifen). The mutant allele frequency (MAF) increased further in the 4 BCs treated with 2nd line ET (2:tamoxifen, 2:exemestane) and further still in the 1 BC who received 3rd line exemestane. 0/6 patients with ESRM responded to subsequent ET. Allele-specific rtPCR and ER-ISMD have been used to validate these findings and also identified low frequency ESRM clones in the sequential samples prior to the development of clinical resistance, that were not reported by NGS. Both methods have also been applied to screen tissues from patients in cohort B, where ESRMs have also been identified in recurrent samples. Complete analysis is currently ongoing. Conclusions: · ESRMs develop and expand in some BCs as a mechanism for acquired resistance to ET and are associated with a lack of response to subsequent standard ETs. · Allele-specific rtPCR can detect ESRMs and is more cost-effective and easier to use than NGS for ER mutation analysis. · Some ESRMs predate clinical resistance. · ER-ISMD is a novel approach that allows for identification and visualisation of the distribution of mutant clones in morphologically intact FFPE tissue. · ER-ISMD has the potential to become a clinically useful tool to help direct the use of 2nd line ET in routine care. Citation Format: Martinez-Perez C, Turnbull AK, Tanioka M, Fernando A, Renshaw L, Keys J, Wheless A, Garrett A, Parker J, He X, Sims AH, Carey LA, Perou CM, Dixon JM. Tracking ESR1 mutation clonal evolution in breast cancer using in situ mutation detection [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 P5-04-14.

ISY3-4 - Issue to be solved in the near future to determine optimal sequential endocrine therapy in metastatic breast cancer

Main objective in palliative therapy for patients with metastatic breast cancer (MBC) is prolonged survival and maintenance of quality of life. In ER-positive/HER2-negative MBC, sequential endocrine therapy is one of the most important treatment strategy for patients who have hormone-responsive and no life-threatening disease. However, the optimal sequential endocrine therapy is not established. Aromatase inhibitor, selective ER modulator, selective ER down-regulator and CDK4/6 inhibitor + aromatase inhibitor are candidates as 1st line endocrine therapy for postmenopausal patients. There is also no clear guidance on subsequent treatment. From the results of several clinical trials, it may be better to sequentially use alternate drugs with different mechanism of action in sequential endocrine monotherapy. However, the advent of CDK4/6 inhibitors have resulted in a paradigm shift in the treatment of ER-positive/HER2-negative metastatic breast cancer. In this presentation, I would like to discuss about 4 issues to be solved in endocrine therapy for postmenopausal ER-positive/HER2-negative metastatic breast cancer. First, should CDK4/6 inhibitor in combination with endocrine agent be used as part of sequential endocrine therapy for all patients? Second, whether CDK4/6 inhibitor are more effective for use in 1st line therapy or subsequent treatment? Third, when using a CDK4/6 inhibitor after 1st line endocrine monotherapy, should it be changed to another endocrine agent or the same endocrine drug? Fourth, what is the optimal treatment in patients who have progressed during or after CDK4/6 inhibitor administration?

Abstract P4-03-01: Causes of endocrine therapy resistance: An in-depth genomic analysis of resistant multidrug ER+ breast cancers

Abstract Background: 70% of all breast cancers (BCs) are ER+. Not all ER+ cancers respond to endocrine therapy (ET) and many eventually develop resistance. The aim was to perform in-depth genomic analysis of both primary resistant BCs, that do not respond to ET, and cancers which progress (&amp;gt;40% increase in size) after an initial response as they acquire resistance (AQR) to ET. Methods: A unique series of 48 post-menopausal women with ER+ BC received neoadjuvant ET using letrozole (L) or anastrozole (A) (mean treatment duration 17 months, range 3-67). 13/48 received up to 4 lines of ET. 12/48 responded to A or L, 16/48 had primary resistance and 20/48 had AQR. Of 20 with AQR, 13 had 2nd line ET with A or tamoxifen (T). 6 had 3rd line ET with exemestane (E) and 1 had 4th line megestrol acetate (MA). Serial RNA &amp; DNA from 3-5 cancer samples/patient (226 samples) had Ribo0-RNAseq, DNA exome sequencing and somatic mutation detection using UNCeqR. We have data so far on 29 patients: 5 responders, 4 with primary resistance and 20 AQR, the full cohort will be complete shortly. Results: ESR1 Mutations (ESRM): 1/5 responders had an ESRM (E380Q) at diagnosis. This clone disappeared with response to L. 5/20 patients with AQR (25%) had clonal expansion of an ESRM during 1st line ET (L:4, A:1). 4 had a chr6:152419926[lowbar]A:G (D538G) ESRM and 1 had a novel ESRM. Of the 5 with ESRM acquired during 1st line ET, the mutant allele fraction (MAF) increased further in the 4 who had 2nd ET (3:T, 1:E) and increased further for the 2 who had 3rd line E. ESR1 Amplification (ESRA): 5 patients developed ESRA. 3/5 developed ESRA on 2nd or 3rd line E that was not present on AQR to 1st line L or A and 2nd line T. The other 2 developed ESRA on L. 2/5 with ESRA had concomitant CYP19A1 amplification. One patient with ESRA that developed on 3rd line E subsequently responded to MA. No patients with primary resistance to 1st line ET had an ESRM or ESRA. PIK3CA mutations (PIK3M): 5/20 with AQR had PIK3M (25%). 3/7 had PIK3M at diagnosis and in 3 MAF increased between 1st and 2nd line ET. 2/7 developed PIK3M when resistant to 2nd line ET, 1 of the 2 had ESRA. 2 patients responsive to L had PIK3M at diagnosis and MAF decreased with therapy. Other Mutations: Unique mutations with limited commonality developed and new clones expanded in the remaining cancers during primary and acquired resistance. Clonality analysis of AQR samples to different ETs showed proliferation of specific clones, characterised by novel sets of mutations, which typically became the dominant clone at the time of resistance to a particular agent. Summary: 13/20 with acquired resistance had ESRM, ESRA, or PIK3M in resistant tumours: 1 had all 3, 2 ERSM + ESRA, 1 ERSA + PIK3CA, 4 ESRM only, 2 ESRA only and 3 had PIK3M only. Conclusions: • Endocrine resistance is complex • ESRM or ESRA is uncommon at diagnosis and does not explain primary ET resistance • ESRM (in particular the D538G mutation) occurs in one-third of patients with acquired resistance. 2nd line ET results in clonal selection and expansion of ESRM cells. Assessing recurrences for ESRM by in situ detection has clinical utility • ESRA is only seen in heavily ET-pre-treated tumours, with its significance being unknown. Citation Format: Dixon JM, Turnbull AK, Tanioka M, Wheless A, Garrett A, Martinez-Perez C, Parker J, He X, Sims AH, Thomas JS, Carey LA, Perou CM. Causes of endocrine therapy resistance: An in-depth genomic analysis of resistant multidrug ER+ breast cancers [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 P4-03-01.

Abstract P1-09-20: An optimized workflow to analyze ESR1 mutations in both circulating cell-free and circulating tumor cell DNA by digital PCR

Abstract Background In metastatic breast cancer (MBC) patients ESR1 mutations (mESR1) in cell-free DNA (cfDNA) have been related to endocrine therapy (ET) resistance. Such mutations might also be detectable in circulating tumor cells (CTCs). Mutation detection in small amounts of cfDNA and in CTCs in a background of leukocytes is highly challenging. The current study evaluated how to reliably investigate mESR1 status in such minute amounts of cfDNA and in DNA from CellSearch-enriched CTCs. Materials &amp; Methods Plasma (200 µL) and matched CellSearch-enriched CTC fractions of 7 healthy blood donors (HBD) and 29 MBC patients at baseline and after ET (≥ 5 CTC/7.5 mL) were evaluated. cfDNA was isolated from plasma with the QIAamp CNA kit and CTC-enriched DNA with the AllPrep kit (Qiagen). mESR1 status in both cfDNA and CTC-enriched DNA fractions was compared with or without whole genome amplification (repli-g WGA, Qiagen) or ESR1 target specific amplification. Quantitative PCR (qPCR) for wild type (WT) ESR1 was used to control the number of WT copies loaded into the chips for digital PCR (dPCR) analysis. The variant allele frequencies (VAF) of hotspot mutations for ESR1 (D538G, Y537S, Y537C and Y537N) were evaluated with mutation-specific Taqman assays by chip-based dPCR (QuantStudio 3D, Thermo Fischer Scientific). Results To allow inclusion of as many samples as possible, we successfully downscaled the volume of required plasma from 1 mL to 200 µL as this resulted in the same VAF. Sample-type specific thresholds for mESR1 presence were established (2% for the cell-free plasma samples, at which percentage all HBDs were negative, and 0.5% for the CTCs to allow identification of one mutated CTC-specific copy in a background of ~1,000 leukocytes). WGA was unable to adequately amplify fragmented cfDNA, resulting in a too low DNA yield. However, locus-specific target pre-amplification of a 136 bp fragment covering all 4 different mutations followed by mutant specific dPCR performed well for both cfDNA and CTC DNA, but only if the loading of the pre-amplified product into the dPCR chips was optimized by qPCR for the number of WT ESR1 copies. The most optimal results for dPCR data interpretation were obtained after: 1. including at least one positive sample in each dPCR session; 2. using a “safe loading window”, 3. loading and reading chips at least twice in QuantStudio 3D ; 4. critically evaluating the contribution by a non-specific “comet effect”; and 5. after loading the data in the software, performing at least two independent data analyses to exclude intra-observer variations. Summary Here we describe our workflow to assess mESR1 in a limited amount of plasma cfDNA or CellSearch enriched CTC DNA. This workflow has been successfully used to investigate the mESR1 VAF status in DNA from matched CTC DNA and cfDNA of MBC patients before start of 1st line endocrine therapy and at progression (see also abstract number 851017). Citation Format: Vitale SR, Sieuwerts AM, Helmijr J, Beije N, van der Vlugt – Daane M, Foekens JA, Sleijfer S, Jansen MPHM, Martens JWM. An optimized workflow to analyze ESR1 mutations in both circulating cell-free and circulating tumor cell DNA by digital PCR [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 P1-09-20.

Meta-analysis of clinical outcomes to second-line endocrine therapy for visceral and non-visceral metastases.

568 Background: A previous meta-analysis reported that patients with hormone receptor-positive visceral metastases (VMs) who respond to 1st-line endocrine therapy (ET) benefit for as long as those ...

PCN31 - Overall survival in post-menopausal women with hr+/her2- metastatic breast cancer treated with 1st-line endocrine therapy vs. Chemotherapy

PCN31 - Overall survival in post-menopausal women with hr+/her2- metastatic breast cancer treated with 1st-line endocrine therapy vs. Chemotherapy

P168 Time-to-failure in 1st-line endocrine therapy with ER+/HER2−metastatic breast cancer

P168 Time-to-failure in 1st-line endocrine therapy with ER+/HER2−metastatic breast cancer

Treatment of hormone positive uterine leiomyosarcoma with aromatase inhibitors.

BackgroundAromatase inhibitors (AIs) have not been used consistently as part of the management of hormone receptor positive uterine leiomyosarcomas (ULMS). As a result, the published data regarding the efficacy of AIs in this subtype of ULMS are sparse.MethodsWe performed a retrospective electronic medical record review of patients with ULMS treated with an AI, in the 1st or the 2nd line setting, at the Sarcoma Unit of the Royal Marsden Hospital between 2001 and 2012. We assessed progression-free survival (PFS), objective response and toxicities and explored the correlation of the intensity of the hormone receptor status, as well as of the grade with PFS.ResultsSixteen patients with measurable advanced ULMS were treated with an AI in our unit. All of them were oestrogen receptor (ER) and progesterone receptor (PgR) positive. Letrozole was used in all patients as 1st line endocrine therapy, while exemestane was mainly prescribed as 2nd line (83%). Median PFS in 1st line was 14 months (95% CI: 0 – 30 months), and prolonged PFS was more likely to be observed in patients with low grade compared to high grade ULMS (20 months vs. 11 months), and in moderately/strongly ER positive compared to weakly ER positive ULMS (20 months vs. 12 months). Best response was partial response (PR) in 2/16 patients (12.5%) and clinical benefit (CB), defined as complete response (CR) + PR + stable disease ≥6 months, was observed in 10/16 patients (CB rate (CBR) 62.5%). Median duration of 2nd line was 3 months and median PFS was not reached. The 1-year progression-free rate for the 2nd line AI was 80%. Best response was PR in one patient and CBR was 50%. AIs were well tolerated in both lines of treatment.ConclusionsIn this population of patients with hormone positive ULMS, AIs achieved a significant CBR (62.5%) in 1st line, which was retained in 2nd line (CBR: 50%). The relatively prolonged median PFS (14 months), along with the favourable toxicity profile could place AIs among the first choices of systemic treatment in hormone positive ULMS, preferably in strongly positive (>90%), and/ or low grade and low volume disease.

Hormonal therapies in young breast cancer patients: when, what and for how long?

Breast cancer in young women (<40 years) is a rare and complex clinical and psychosocial condition, which deserves multidisciplinary and personalized approaches. In young women with hormone-receptor positive disease, 5 years of adjuvant tamoxifen, with or without ovarian suppression/ablation, is considered the standard endocrine therapy. The definitive role of adjuvant aromatase inhibitors has still to be elucidated: the upcoming results of the Tamoxifen and EXemestane Trial (TEXT) and Suppression of Ovarian Function Trial (SOFT) trials will help understanding if we can widen our current endocrine therapeutic options. The optimal duration of adjuvant endocrine therapy in young women also remains an unresolved issue. The recently reported results of the ATLAS and aTToM trials represent the first evidence of a beneficial effect of extended endocrine therapy in premenopausal women and provide an important opportunity in high-risk young patients. In the metastatic setting, endocrine therapy should be the preferred choice for endocrine responsive disease, unless there is evidence of endocrine resistance or need for rapid disease and/or symptom control. Tamoxifen in combination with ovarian suppression/ablation remains the 1st-line endocrine therapy of choice. Aromatase inhibitors in combination with ovarian suppression/ablation can be considered after progression on tamoxifen and ovarian suppression/ablation. Fulvestrant has not yet been studied in pre-menopausal women. Specific age-related treatment side effects (i.e., menopausal symptoms, change in body image and weight gain, cognitive function impairment, fertility damage/preservation, long-term organ dysfunction, sexuality) and the social impact of diagnosis and treatment (i.e., job discrimination, family management) should be carefully addressed when planning long-lasting endocrine therapies in young women with hormone-receptor positive early and advanced breast cancer.

PR and Ki67 in primary tumors and metastatic sites as biomarkers for benefit from endocrine therapy (ET) in metastatic breast cancer (mBC).

e11521 Background: Commonly used biomarkers (ER, PR, HER2, Ki67) are thought to identify BC subtypes with different sensitivity to ET, but data on this are scarce for the metastatic setting, where changes in receptor status between primary tumor (T) and matched metastases (M) are reported. We investigate PR and Ki67 on T and M as predictors of clinical benefit from 1st line ET in mBC. Methods: We identified mBC patients (pts) treated in our Center with 1st line ET (2002-11), excluding those receiving concomitant chemotherapy (CT) or trastuzumab or pretreated with &gt;2 lines of CT. PR and Ki67 were scored as IHC percentage of positive cells, with a cut-off of 20% for high vs low. Clinical benefit was evaluated by time-to-progression (TTP). Results: We identified 137 pts, median age 58 (29-85), only 28% with visceral metastases. ER was &gt;50% in 94%, HER2+ in 17.5%. With 93% receiving an aromatase inhibitor, median TTP was 14 months (median follow-up 43 months). In 34 pts with Ki67 available from T and M a strong correlation between the 2 was shown (Spearman: 0.69, p&lt;.0001), confirming little variation. A shorter median TTP (10 vs 17 months, n=113; Wilcoxon p=0.006) was seen in pts with Ki67 &gt;20% on T (with a similar trend on M, n=58; p=0.06). In 48 pts with PR scored on T and M only a weak trend for correlation was found, with a discordant classification (≤ or &gt;20%) in 44%. More than the score on T (n=118), PR on M (n=64) was a strong predictor of median TTP: 12 months for PR ≤20% vs 22 months for PR &gt;20% (p=0.02). Pts with PR≤20% + Ki67&gt;20% on M had a median TTP of only 4 months, vs 21 months for PR&gt;20% + Ki67≤20%, vs 14 months for either PR&gt;20% or Ki67≤20% (p=0.006). In a multivariate Cox analysis with clinical data and biomarkers from T, visceral disease and HER2 positivity were significantly associated with the risk of progression (HR 2.22 and 2.07, respectively). With biomarkers from M, the risk of progression correlated with relapse ≤5 vs &gt;5 years from surgery (HR 3.48) and PR ≤20% (HR 2.47, p=0.01). Conclusions: In an ER-high population, PR &gt;20% on M identifies pts with a long TTP on ET. Ki67 on T or M can also contribute in estimating the expected benefit, but an independent prognostic role could not be fully confirmed in this small cohort.

Abstract P2-14-04: A Phase Ib Dose Escalation Trial of RO4929097 (a γ-secretase inhibitor) in Combination with Exemestane in Patients with ER + Metastatic Breast Cancer.

Abstract Background: RO4929097 is a potent and oral selective inhibitor of γ-secretase (GSI), producing inhibitory activity of Notch 1–4 signaling in tumor cells. Preclinical studies have demonstrated synergism of GSIs in combination with endocrine therapy, in ERα-positive xenografts. This suggests that optimal treatment of ER+ BC would benefit from an antiestrogen and GSI combination. Materials and Methods: To explore the safety, tolerability and preliminary antitumor activity of Exemestane (25 mg/d) with R04929097 combination, we conducted a Phase Ib trial in patients with ER+/ HER2− MBC, whose disease relapsed during treatment with or within 6 months of discontinuation of an adjuvant nonsteroidal aromatase inhibitor or Tamoxifen, or whose MBC progressed during treatment with 1st or 2nd line endocrine therapy. Goserelin (3.6 mg q28 days Sub-Q) was given to all premenopausal patients. R04929097 was administered orally daily for 3 consecutive days, followed by 4 days off on a 21 day cycle. Doses of R04929097 were escalated on a standard 3+3 design over 5 doses (20, 30, 45, 90, and 140 mg). Patients were fully evaluated for dose limiting toxicity (DLT) for 3 weeks. Patients were treated until disease progression or occurrence of unacceptable toxicity. Results: A total of 15 patients were enrolled. Median age was 56; average number of chemotherapies received in the adjuvant or metastatic setting was 3.3. Eleven patients had received adjuvant endocrine therapy. One patient received this as 1st line endocrine therapy, eleven patients received this study as 2nd line endocrine therapy; and three patients received this study as 3rd line endocrine therapy in the metastatic setting. Of the 14 patients evaluable, 1 had a partial response, 6 had stable disease, and 7 had progressive disease. All patients have discontinued the study at this time, 11 due to progression, 2 due to toxicity, and 1 withdrew after beginning protocol therapy. Twenty percent of patients had stable disease for six months or greater. Of the patients with stable disease for six months, one patient progressed at 9 months and 2 patients progressed at 10 months. The most common toxicities were nausea (73.3%), anorexia (60%), hyperglycemia (53.3%), hypophosphatemia (46.7%), fatigue (66.7%), and cough (33.0%). Grade 3 toxicities were uncommon and included hypophosphatemia (13.0%) and rash (6.3%). There were no grade 4 toxicities. Rash was the only DLT and was seen at 140 mg. Conclusion: The combination of R04929097 and Exemestane was overall well tolerated, but MTD was not determined as access to drug ended. Further studies with GSIs in combination with endocrine therapy are warranted on the basis of a favorable safety profile and preliminary evidence of stable disease seen in patients with ER+ MBC refractory to previous endocrine therapies. PK, PD and biomarker analysis is ongoing. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-14-04.