Prior Aromatase Inhibitor Research Articles

Real-world (RW) elacestrant use patterns and therapeutic outcomes in patients (pts) with hormone receptor-positive (HR+)/HER2-negative advanced breast cancer (aBC).

1071 Background: Elacestrant was the first novel endocrine therapy (ET) to receive FDA approval in over two decades. In the EMERALD study, pts with ESR1-mutant ( ESR1m) HR+/HER2-negative aBC had a median progression free survival (PFS) of 3.8 months (mos). Here, we use a large clinical-genomic database to assess the RW use of elacestrant and examine the impact of line of therapy (LOT) and number of ERS1m on pt outcomes. Methods: Pts with HR+/HER2- aBC were identified via the GuardantINFORM database; all pts with ESR1m detected on circulating tumor DNA (ctDNA) testing done in routine clinical care and treated with elacestrant after the FDA approval date were included. Real-world time to treatment discontinuation (TTD) and time to next treatment (TTNT) were used as proxies for PFS (measured in mos). For TTD/TTNT, Kaplan-Meier curves and median time-to-event with 95% confidence intervals (CI) were used. For outcomes specific to single versus >1 ESR1m, only pts with an ESR1m detected within the 6 months prior to elacestrant start were included. Results: 418 aBC pts were treated with elacestrant, with a median age of 62 years. Elacestrant was used across metastatic LOT (2nd: 12%, 3rd: 18%, 4tH: 17%, 5th+: 53%). Considering all prior therapies, pts commonly received prior aromatase inhibitors (AI) (89%), CDK4/6i (73%), fulvestrant (63%), and chemotherapy (49%). Of 312 pts with testing within 6 months of elacestrant start, 56% harbored a single ESR1m, with a maximum of 11 ESR1m detected in a single patient. TTD was 5.4 mos (95% CI: 4.2 - not reached [NR]) and TTNT was 6.2 mos (95% CI: 5.7 - NR); most pts were censored at the time of analysis (65% for TTD, 71% for TTNT). There were no significant differences in TTD or TTNT based on number of prior LOT or number of ESR1m mutations (Table 1). Data was not yet mature to assess differences in outcomes based on prior ET use, duration of prior CDK4/6i exposure, specific ESR1m, or co-occurring alterations. Conclusions: Using a clinical-genomic database, we present early RW insights of aBC pts treated with elacestrant. Initial outcomes, as assessed via TTD and TTNT, exceed the PFS reported in the EMERALD trial, perhaps due to multiple factors impacting patient selection and restaging protocols, which can differ in prospective trials versus routine clinical care. Factors such as prior LOT and number of ESR1m did not impact patient outcomes; additional factors such as prior ET use, duration of CDK4/6i treatment, specific ESR1m, and co-occurring mutations will be assessed as data matures. [Table: see text]

Abstract PO3-05-08: Updated results from VERITAC evaluating vepdegestrant, a PROteolysis TArgeting Chimera (PROTAC) estrogen receptor (ER) degrader, in ER–positive/human epidermal growth factor receptor 2 (HER2)–negative advanced breast cancer

Abstract Background: Vepdegestrant (ARV-471) is an oral PROTAC ER degrader with activity toward wild-type and mutant ER. The phase 2 expansion (VERITAC) of a phase 1/2 study (NCT04072952) tested 2 vepdegestrant doses (200 mg once daily [QD] and 500 mg QD) in heavily pretreated patients with ER+/HER2- advanced breast cancer. Vepdegestrant 200 mg QD was selected as the phase 3 monotherapy dose based on comparable efficacy and favorable tolerability vs 500 mg QD and robust ER degradation (data cutoff: Jun 6, 2022). We present updated data for the vepdegestrant 200 mg QD cohort after 12 additional months of follow-up. Methods: Vepdegestrant was administered to patients with ER+/HER2- locally advanced/metastatic breast cancer who had received ≥1 prior endocrine therapy for ≥6 months, ≥1 cyclin-dependent kinase (CDK)4/6 inhibitor, and ≤1 chemotherapy regimen. The primary endpoint was clinical benefit rate (CBR; rate of confirmed complete response, partial response, or stable disease ≥24 weeks). Results: As of Jun 6, 2023, 35 patients received vepdegestrant 200 mg QD; 34 (97.1%) were female and median age was 63 y (range: 42–79). Patients had received a median of 4 prior regimens (range: 1–9) in all settings and 3 prior regimens (range: 0–7) in the metastatic setting; 100% had prior CDK4/6 inhibitors, 88.6% had prior aromatase inhibitors, 74.3% had prior fulvestrant, and 74.3% had prior chemotherapy (45.7% in metastatic setting). CBR with vepdegestrant 200 mg QD was 37.1% (95% CI: 21.5–55.1) in all evaluable patients (n=35) and the objective response rate was 8.3% (95% CI: 1.0–27.0) among 24 patients with measurable disease at baseline. Median progression-free survival in all evaluable patients was 3.5 months (95% CI: 1.8–8.2). As of the data cutoff date, 14 patients in the 200 mg QD cohort received treatment for ≥24 weeks (4 for ≥48 weeks) with 1 patient ongoing. No patients required a dose reduction due to a treatment-emergent adverse event (TEAE); 2 (5.7%) patients had a TEAE that led to vepdegestrant discontinuation (grade 3 QT prolongation and grade 3 anemia). The most common treatment-related adverse events (≥10%) were fatigue (43%), hot flush (20%), nausea (17%), arthralgia (11%), increased aspartate aminotransferase (11%), and increased blood alkaline phosphatase (11%); all were grade 1/2. Substantial on-treatment decreases in mutant ESR1 circulating tumor DNA levels were observed with vepdegestrant 200 mg QD and sustained for multiple treatment cycles. Conclusions: With 12 months of additional follow-up from the first data report, durable clinical activity with vepdegestrant 200 mg QD was seen in heavily pretreated patients with ER+/HER2- advanced breast cancer, in addition to sustained reduction in circulating mutant ESR1 tumor DNA levels. Vepdegestrant 200 mg QD continued to show a favorable safety profile. The ongoing global, randomized phase 3 VERITAC-2 study (NCT05654623) is evaluating vepdegestrant 200 mg QD vs intramuscular fulvestrant in patients with ER+/HER2- advanced breast cancer after prior combination CDK4/6 inhibitor therapy and endocrine therapy. Citation Format: Sara Hurvitz, Anne Schott, Cynthia Ma, Rita Nanda, George Zahrah, Natasha Hunter, Antoinette Tan, Melinda Telli, Jesus Anampa Mesias, Rinath Jeselsohn, Pamela Munster, Eric Zhi, Elizabeth Duperret, Cecile Mather, Erika Hamilton, Hyo Han. Updated results from VERITAC evaluating vepdegestrant, a PROteolysis TArgeting Chimera (PROTAC) estrogen receptor (ER) degrader, in ER–positive/human epidermal growth factor receptor 2 (HER2)–negative advanced breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-05-08.

Abstract PS15-01: A first-in-human phase 1 study of SIM0270, a brain-penetrant oral selective estrogen receptor degrader (SERD), in patients with ER+/HER2- locally advanced or metastatic breast cancer

Abstract Background: ER+/HER2- breast cancer is the most prevalent subtype, and endocrine-based therapy is the standard treatment. SIM0270 is a brain-penetrant and highly potent oral SERD that has demonstrated ER degradation and robust antitumor activity across various preclinical models, including those with intracranial xenograft tumors. Methods: This Phase 1 study evaluates the safety, pharmacokinetics and preliminary anti-tumor activity of SIM0270 as monotherapy and/or in combination with palbociclib or everolimus in patients with HR+/HER2- advanced or metastatic breast cancer. The primary objective of the phase 1a study, which consisted of the dose escalation stage and the dose expansion stage, is to determine the maximum tolerated dose (MTD) and/or recommended phase 2 dose (RP2D) of SIM0270 as monotherapy. A Bayesian Optimal Interval design (BOIN) was adopted. SIM0270 was administered orally daily in 28-day cycles. Here we report preliminary monotherapy data. Results: As of May 22nd 2023, 45 female patients were enrolled, receiving SIM0270 at dose levels of 10 mg (n=4), 30 mg (n=4), 60 mg (n=9), 90 mg (n=6), 120 mg (n=11), 200 mg (n=5), or 300 mg (n=6). The median age was 56 years (range, 40-73) and ECOG performance status was 0 (18%) or 1 (82%). Most patients were heavily pretreated, with a median of 2 prior endocrine-based therapies (range, 0-5) and a median of 2 prior chemotherapies (range, 0-8). Thirty-one patients (69%) received prior fulvestrant, 42 (93%) received prior aromatase inhibitors, and 28 (62%) received prior CDK4/6 inhibitors. Visceral metastases were present in 33 patients (72%), and brain metastases in 7 patients (16%). The most common TEAEs were sinus bradycardia (51%), anemia (38%), hypalbuminaemia (31%), hypercholesterolaemia (24%), urinary tract infection (24%), asthenia (24%), electrocardiogram (ECG) QT prolonged (24%), and dizziness (22%). Most of the TEAEs were Grade 1-2. Grade 3 TRAEs were ECG QT prolonged, gamma-glutamyltransferase(γ-GT) increased and dizziness in 2 patients each. All AEs were manageable with dose interruption or reduction, except only 1 patient discontinued treatment of SIM0270 due to TRAE (Grade 3 γ-GT increased). Four patients experienced dose-limiting toxicities (DLTs): 1 with Grade 3 ECG QT prolonged at 200mg dose level, 1 with Grade 3 ECG QT prolonged and 2 with Grade 3 dizziness at 300mg dose level. All DLTs were resolved with dose interruption then reduction. The MTD of single-agent SIM0270 was established as 200mg QD. Pharmacokinetic analysis revealed a T1/2 of approximately 70 hours, and the AUC and Cmax increased in an approximately linear manner with dose escalation. Concentration in cerebrospinal fluid was measured in 1 patient after 41 days treatment of SIM0270, which is consistent with preclinical data and suggested high concentration of SIM0270 in the brain of patients. Among 31 response evaluable patients (per RECIST 1.1 criteria), 4 PRs (3 unconfirmed) were observed, yielding an ORR of 12.9%. Brain lesions were all stable in 4 evaluable patients per RANO-BM criteria. In patients with ESR1 mutations at baseline and samples available for analysis, 4/6(67%) exhibited a reduction or loss of mutant ESR1 upon SIM0270 treatment. Conclusions: Single-agent SIM0270 was well tolerated and showed favorable antitumor activity in heavily pretreated advanced or metastatic ER+/HER2- breast cancer patients, including those previously treated with CDK4/6 inhibitors and fulvestrant. Phase 1a dose expansion with single-agent SIM0270 is ongoing, and the RP2D will be determined based on further accumulative data of tolerability and efficacy. (NCT05293964) Citation Format: Jiong Wu, Jian Zhang, Qingyuan Zhang, Yuping Sun, Hongtao Li, Yongmei Yin, Yehui Shi, Wenfeng Li, Yunjiang Liu, Min Yan, Chen Yang, Lili Zhu, Yang Yang, Liting Xue. A first-in-human phase 1 study of SIM0270, a brain-penetrant oral selective estrogen receptor degrader (SERD), in patients with ER+/HER2- locally advanced or metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS15-01.

Abstract PO1-04-10: Body Mass Index and Treatment Efficacy in advanced Luminal Breast Cancer: Insights from the GEICAM/2013-02 (PEARL) trial

Abstract Background: Endocrine therapy (ET) and treatment directed against molecular targets (CDK 4/6, PI3K, mTOR) constitute the basis of initial treatments for patients with advanced luminal breast cancer. Most of these treatments are oral and have been developed at a fixed dose, without weight adjusted dosing. There is little evidence on the influence that patients’ weight might have on clinical outcomes of these oral drugs in the context of a randomized clinical trial. The present study analyzes the potential impact of the weight of patients treated in the two cohorts of the PEARL trial (NCT02028507) on Progression-Free Survival (PFS), Overall Survival (OS) and the incidence of side effects in each treatment arm. Methods: GEICAM/2013-02 (PEARL) is a multicenter, phase III randomized clinical trial that enrolled patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer (MBC) who progressed to a prior aromatase inhibitor. Patients were randomized 1:1 to receive ET + palbociclib or capecitabine. Patient weight was assessed based on baseline body mass index (BMI) categories: normal (BMI ≤25 Kg/m2), overweight (BMI 25-29.9 Kg/m2) and obesity (BMI ≥30 Kg/m2). Cox's stratified proportional hazard model was used for survival analysis. Adverse events were assessed and graded according to National Cancer Institute common terminology criteria for adverse events (NCI-CTCAE) version 4.0. Results: A total of 600 patients were included in the study and all were evaluable for the weight-based analysis, including 301 in the ET +palbociclib arm and 299 in the capecitabine arm. The distribution of patient’s weights is shown in Table 1. For the Intention-to-treat (ITT) population, no significant difference in the median OS was found between the different weight categories (Normal: 32.8 months vs overweight: 31.9 months, [p=0.467]; obese: 32 months [p=0.407]). Specifically, for patients with normal weight, the median PFS was 9.3 months in the ET + palbociclib group compared to 9.0 months in the capecitabine group (hazard ratio (HR) 0.83, 95% confidence interval [CI]: 0.61-1.13; p=0.23). In the overweight group, the PFS was 7.5 months in the ET+palbociclib group and 11.1 months in the capecitabine group (HR 1.17, 95% CI: 0.87-1.58; p=0.30) while for the obese group, the PFS was 5.7 months vs 11.7 months (HR 1.14, 95% CI: 0.82-1.59; p=0.43), respectively. No substantial differences in the incidence of grade ≥ 3 events were observed when considering weight categories in the different treatment groups (capecitabine arm (Normal: 60%, Overweight: 70.4%, Obese: 61.6%) and ET+palbociclib arm (Normal: 74.5%, Overweight: 76.1%, Obese: 51.6%). Conclusions: Our findings, despite not finding statistically significant differences, suggest a potentially clinically relevant trend towards improved PFS with capecitabine in overweight and obese patients compared to those receiving palbociclib plus ET. The impact of weight on the outcomes with fixed-dose oral drugs warrants further investigation in future studies. Table 1. Citation Format: Manuel Alva, Sara López-Tarruella, Christoph Zielinski, Manuel Ruíz - Borrego, Nicholas Turner, Eva Ciruelos, Montserrat Muñoz, Begoña Bermejo, Mireia Margelí, Antonio Antón, Zsuzsanna Kahan, Tibor Csöszi, Maribel Casas, Laura Murillo, Serafin Morales Murillo, Emilio Alba, Einav Nili-Gal Yam, Angel Guerrero, Lourdes Calvo, Juan de la Haba-Rodríguez, Manuel Ramos, Isabel Álvarez, Andrés García-Palomo, María Koehler, José Ángel García-Sáenz, J. Ignacio Chacón, Claire Swift, Christiane Thallinger, Miguel Gil-Gil, Miguel Martín. Body Mass Index and Treatment Efficacy in advanced Luminal Breast Cancer: Insights from the GEICAM/2013-02 (PEARL) trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-04-10.

Capivasertib: A Novel AKT Inhibitor Approved for Hormone-Receptor-Positive, HER-2-Negative Metastatic Breast Cancer.

To review the pharmacology, efficacy, and safety of capivasertib for the treatment of adults with hormone receptor-positive, HER2-negative (HR+/HER2-) locally advanced or metastatic breast cancer with 1 or more PIK3CA/AKT1/PTEN alterations. A literature search was conducted using PubMed and MEDLINE databases, published abstracts, and studies from ClinicalTrials.gov between 2003 and February 2024. Keywords included capivasertib, AZD5363, PI3K/AKT/mTOR pathway, and breast cancer. All applicable publications, package inserts, meeting abstracts, and clinical trials with capivasertib were reviewed. Capivasertib is a first-in-class inhibitor of 3 isoforms of AKT (AKT-1, AKT-2, and AKT-3) which is an essential component in the PI3K/AKT/mTOR signaling pathway involved in oncogenesis. In the phase III CAPItello-291 trial, capivasertib in combination with fulvestrant (C+F) demonstrated improved progression-free survival (PFS) (7.3 vs 3.1 months) compared with placebo-fulvestrant (P+F) cohort in AKT-altered pathway patients who had progressed through prior aromatase inhibitor. The most common adverse reactions of any grade reported in the C+F group were diarrhea, cutaneous skin reactions, nausea, fatigue, and vomiting. HR+/HER2- advanced breast cancer patients experience progression following endocrine therapies and cyclin-dependent kinase (CDK) 4/6 inhibitors. Capivasertib is a viable treatment option for patients with PIK3CA/AKT1/PTEN activating mutations following progression on endocrine-based regimens in the metastatic setting or recurrence within 12 months of completing adjuvant therapy. Integration of capivasertib into clinical practice is ongoing; intermittent dosing and favorable toxicity are attractive for future novel combination prospective trials.

Abstract OT2-01-03: ELEVATE: A phase 1b/2, open-label, umbrella study evaluating elacestrant in various combinations in women and men with metastatic breast cancer (mBC)

Abstract Background: Elacestrant demonstrated significantly prolonged progression-free survival (PFS) and a manageable safety profile compared with standard of care endocrine therapy in the phase 3 EMERALD trial that enrolled patients with estrogen-receptor positive (ER+)/HER2− mBC following disease progression on prior endocrine and cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) therapy. Benefit was observed in the overall population and in patients with ESR1 mutations. Combining elacestrant with targeted agents utilized in combination with endocrine therapy in mBC is of therapeutic interest. Methods: ELEVATE is a phase 1b/2 trial designed to evaluate the combination of elacestrant with alpelisib, everolimus, palbociclib, abemaciclib, or ribociclib. Eligible patients (pts) are women or men with ER+/HER2− locally advanced or mBC, measurable disease per RECIST v1.1 or ≥1 lytic or mainly lytic bone lesion, ECOG PS ≤1, no inflammatory breast cancer or uncontrolled central nervous system metastases, in addition to treatment-arm specific eligibility criteria as detailed below. In the phase 1b portion, pts who have received prior aromatase inhibitor (AI) and CDK4/6i will be enrolled in three 6-patient cohorts for each combination except abemaciclib (under study in a separate trial). Patients will receive elacestrant with the targeted agent at reduced or full doses. The primary endpoint of phase 1b is to determine the recommended phase 2 dose for each combination. Secondary endpoints are safety, pharmacokinetics, pharmacodynamics, and efficacy (objective response rate [ORR], duration of response [DoR], clinical benefit rate [CBR], PFS, and overall survival [OS]). The phase 2 portion will enroll 5 separate arms: A) pts with PIK3CA mutation(s) and prior AI + CDK4/6i: alpelisib + elacestrant, n=50; B) pts with prior AI + CDK4/6i: everolimus + elacestrant, n=50; C) pts with prior AI + CDK4/6i: abemaciclib or ribociclib (investigator’s [inv] choice) + elacestrant, n=60 (30 per combination); D) pts with prior AI only (no CDK4/6i): palbociclib, abemaciclib or ribociclib (inv choice) + elacestrant, n=90 (n=30 per combination); E) pts with no prior systemic therapy: palbociclib or ribociclib (inv choice) + elacestrant, n=90 (n=45 per combination). No prior fulvestrant or chemotherapy is allowed in any arm and no more than 2 prior hormonal therapies are permitted in arms A-D. Prior therapy restrictions apply to the mBC setting or within 12 months of adjuvant therapy. The primary endpoint for the phase 2 portion is the estimation of PFS at 6 months in arms A, B, and C and at 12 months in arms D and E. Secondary endpoints will include ORR, DoR, CBR, PFS, OS, and safety. The Kaplan-Meier method will be used to estimate PFS. Descriptive statistics will be used to evaluate response and safety. Citation Format: Hope Rugo, Aditya Bardia, Javier Cortés, Giuseppe Curigliano, Erika Hamilton, Sara Hurvitz, Sibylle Loibl, Simona Scartoni, Tarek Sahmoud, Krzysztof Grzegorzewski, Nassir Habboubi, Joyce O’Shaughnessy. ELEVATE: A phase 1b/2, open-label, umbrella study evaluating elacestrant in various combinations in women and men with metastatic breast cancer (mBC). [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-01-03.

Adjuvant study of amcenestrant (SAR439859) versus tamoxifen for patients with hormone receptor-positive (HR+) early breast cancer (EBC), who have discontinued adjuvant aromatase inhibitor therapy due to treatment-related toxicity (AMEERA-6).

TPS607 Background: There are currently limited treatment options for patients with HR+ EBC who have discontinued adjuvant treatment with aromatase inhibitors (AIs) due to treatment-related toxicity. Amcenestrant is an optimized oral selective estrogen receptor degrader (SERD) with potent dual activity which antagonizes and degrades the ER resulting in inhibition of the ER signalling pathway. Preliminary clinical evidence from the phase 1/2 AMEERA-1 trial has demonstrated meaningful antitumour activity and a favourable safety profile of amcenestrant in the treatment of HR+ advanced breast cancer (Linden HM, Campone M, Bardia A, et al: Abstract PD8-08: A phase 1/2 study of SAR439859, an oral selective estrogen receptor (ER) degrader (SERD), as monotherapy and in combination with other anti-cancer therapies in postmenopausal women with ER-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (mBC): AMEERA-1. SABCS 2020 PD8-08). Methods: AMEERA-6 is a prospective, randomized, international, double-blind, double-dummy, phase 3 study. 3738 patients will be randomized 1:1 to receive either amcenestrant 200 mg daily or tamoxifen 20 mg daily. Eligible patients are pre-or postmenopausal women or men with HR+ EBC (stage IIB-III) who have received at least 6 months of adjuvant AIs (at least 3 months in the adjuvant setting if they have received prior neoadjuvant AI therapy) and discontinued them within 30 months of initiation due to treatment-related toxicity. Participants will be centrally assessed to have ER+ and/or PgR+ (≥10% positive stained cells) status by immunohistochemistry assay. Prior use of adjuvant CDK4/6 inhibitors are allowed. Patients are eligible irrespective of HER2 status; for patients with HER2-positive disease adjuvant anti-HER2 treatment and chemotherapy must be completed prior to randomization. Stratification factors include: duration of AI therapy, HER2 status, prior chemotherapy, prior CDK4/6 inhibitors, geographic region, and menopausal status. Planned treatment duration is 5 years. Patients will be followed-up for 10 years from randomization. The primary endpoint is invasive breast cancer-free survival (IBCFS). Invasive disease-free survival is a key secondary endpoint, while other secondary endpoints include distant relapse-free survival (RFS), locoregional RFS, overall survival, breast-cancer specific survival, safety, patient reported outcomes and pharmacokinetics. Adherence to treatment is an exploratory endpoint. AMEERA-6 opened for recruitment in January 2022. Clinical trial information: NCT05128773.

Abstract PD15-01: Impact of ESR1 mutations on endocrine therapy (ET) plus alpelisib benefit in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-), PIK3CA-mutated, advanced breast cancer (ABC) who progressed on or after prior cyclin-dependent kinase inhibitor (CDK4/6i) therapy in the BYLieve trial

Abstract PD15-01: Impact of <i>ESR1</i> mutations on endocrine therapy (ET) plus alpelisib benefit in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-), <i>PIK3CA</i>-mutated, advanced breast cancer (ABC) who progressed on or after prior cyclin-dependent kinase inhibitor (CDK4/6i) therapy in the BYLieve trial

CCNE1 mRNA and cyclin E1 protein expression as predictive biomarkers for efficacy of palbociclib plus fulvestrant versus capecitabine in the phase III PEARL study.

1014 Background: The randomized PEARL trial found no superiority of palbociclib plus endocrine therapy over capecitabine in patients (pts) with metastatic HR-positive, HER2-negative breast cancer resistant to prior aromatase inhibitors (Martin M, Ann Oncol 2020). Gene expression analysis showed high CCNE1 mRNA ( CCNE1) conferring relative resistance to palbociclib in the PALOMA-3 trial (Turner N, JCO 2019), but further validation is needed. Cyclin E1 protein (cyclin E1) expression in this context has not been studied in randomized trials. We explored CCNE1 and cyclin E1 as predictive biomarkers in tumor samples from the PEARL study. Methods: Formalin-fixed paraffin-embeded tumor samples were retrieved from pts enrolled in PEARL cohort 2 (palbociclib (PAL) + fulvestrant (FUL) vs capecitabine (CAPE)). We measured CCNE1 using the HTG EdgeSeq Oncology Biomarker Panel (HTG Molecular Diagnostics). Cyclin E1 immunohistochemistry (IHC) staining was performed using specific mouse monoclonal antibody HE12 (Abcam) and scored as percentage of invasive nuclei stained (0-100%). CCNE1 and cyclin E1 correlations were explored using Pearson coefficients. Cox regression models were used for progression free-survival (PFS) analyses using expression levels split by median, to define high ( &gt; median values) vs. low expression. Site of disease and prior chemotherapy were used as confounders in multivariate models. Results: Analyses were conducted in 219 pts (47% receiving PAL + FUL and 53% CAPE) with available tumors, with the analysed patients representative of the overall study. Most samples were from the archival primary (72%), obtained &gt; 5 years before this analysisº (74%). CCNE1 and cyclin E1 were only moderately correlated (r = 0.5). Median CCNE1 was higher in metastatic vs primary (7.37 vs 6.94, p &lt; 0.01), and in luminal B and non-luminal subtypes compared to luminal A (p &lt; 0.001). In patients with high CCNE1 expression, median PFS on CAPE was 10.35 and PAL + FUL was 5.68 (HR = 1.63, 95% CI 1.02-2.59, p = 0.042). In patients with low CCNE1 expression, median PFS on CAPE was 9.43 and PAL + FUL was 8.97 (adjusted HR = 0.93, 95% CI 0.59-1.48, p = 0.762, interaction p = 0.072). Median cyclin E1 protein was higher in luminal B and non-luminal subtypes compared to luminal A (p &lt; 0.01). Cyclin E1 protein expression was not predictive of treatment effect (high cyclin E1 expression CAPE vs PAL + FUL HR = 1.17, low cyclin E1 expression CAPE vs PAL + FUL HR = 1.21, interaction p = 0.977). Conclusions: High tumor CCNE1 mRNA expression identified patients with relative resistance to palbociclib plus fulvestrant, validating prior observations although without statistical significance for interaction. Assessment of Cyclin E1 protein expression did not show predictive value. Investigation treatments to enhance CDK4/6 inhibitor efficacy in tumors with high CCNE1 expression is warranted. Clinical trial information: NCT02028507 .

Real World Experience of Long Term Treatment Outcome in Hormone Receptor-positive Metastatic Breast Cancer with or without Everolimus and Exemestane after Prior Aromatase Inhibitor

Background: Everolimus/exemestane has been shown to improve progression-free survival in patients with endocrine-resistant metastatic breast cancer. The regimen has been well-accepted despite lack of survival benefit. In real-life setting, patients were not well-selected and hence benefit of such treatment may not be as robust. Method: This is a retrospective review of 143 hormone receptor (HR) positive, HER-2 negative MBC patients who progressed on nonsteroidal aromatase inhibitors. Patients who received everolimus/exemestane in any treatment lines (EE group) were compared to patients who never received everolimus (NE group). Primary end point was survival adjusted to prognostic factors. Results: There were 52 patients in EE group and 91 in NE group with mean age of 58.6 years. Median follow-up time was 51 months. Unadjusted median OS was significantly longer in EE [33 vs 25 months, HR 0.66 (95%CI 0.44-0.998); p = 0.049]. In univariate analysis, factors affecting survival included numbers of metastatic sites, bone metastasis, EE treatment and numbers of treatment lines. Independent factors that remained significant in multivariate analysis were treatment lines [HR 0.71 (95%CI 0.63-0.79); p &lt; 0.05] and numbers of metastatic sites. Median numbers of treatment line after NSAI failure was 5.2 vs 3.6 lines in EE and NE, respectively.Conclusion: In this real-life practice data, pts with HR positive, HER-2 negative MBC who had progressed on NSAI, sequential use of multiple treatment regimens of endocrine and chemotherapy is essential to longer survival. Everolimus/exemestane may have contributed, to a lesser extent, to this improvement in survival.

Abstract PD2-06: Clinical outcomes of alpelisib plus fulvestrant in hormone receptor-positive, human epidermal growth factor receptor-2-negative advanced breast cancer with PIK3CA alterations detected in plasma ctDNA by next-generation sequencing: Biomarker analysis from the SOLAR-1 study

Abstract Introduction: The PI3K pathway is often hyperactivated in cancer as a result of an altered PI3K isoform and/or loss of phosphatase and tensin homolog function. Approximately 40% of patients (pts) with hormone receptor-positive (HR+), human epidermal growth factor receptor-2-negative (HER2−) advanced breast cancer (ABC) have tumors with mutations in PIK3CA, which encodes the α-isoform of PI3K, p110α. These mutations are known to cause hyperactivation of the PI3K pathway, which contributes to cell proliferation, drug resistance, and poor prognoses. Alpelisib (ALP) is an α-selective PI3K inhibitor that, in combination with fulvestrant (FUL), prolonged median progression-free survival (mPFS) in pts with HR+, HER2−, PIK3CA-mutant ABC following progression on/after prior aromatase inhibitor in the phase 3 SOLAR-1 trial. In SOLAR-1, prospective PIK3CA mutation testing was performed on tumor tissue using PCR-based assays. Through retrospective analysis, efficacy of ALP was demonstrated in subgroups of pts with PIK3CA alteration(s) in tumor tissue and mutation(s) in ctDNA, detected by next-generation sequencing (NGS) and PCR, respectively. In this exploratory biomarker analysis, we assessed clinical outcomes of pts with PIK3CA alteration(s), detected in ctDNA by NGS.Methods: SOLAR-1 is a phase 3, randomized, double-blind, placebo-controlled study of ALP 300 mg vs placebo taken daily with FUL 500 mg every 28 days + Cycle 1 Day 15 in men and postmenopausal women with HR+, HER2- ABC. Retrospectively, the full exonic region of the PIK3CA gene was sequenced using the Foundation Medicine 324-gene ctDNA panel in plasma ctDNA collected at baseline. mPFS was assessed using Kaplan-Meier methodology per investigator assessment.Results: Of 572 pts in SOLAR-1, 381 pts (66.6%) across both PIK3CA-mutant and nonmutant cohorts had valid plasma ctDNA data. Of these pts, 193 (50.7%) had a PIK3CA alteration; 168 (87%) had PCR-detectable mutations and 147 (76%) had a single alteration. A total of 70 (36%) and 102 (53%) pts had alterations in exons 9 and 20, respectively. ALP plus FUL prolonged mPFS in pts with PIK3CA alterations detected in plasma ctDNA by NGS (n=101; Table). Clinical benefit was also observed in pts with PCR-detectable mutations (n=88), single mutations (n=83), and pts with mutations in exon 9 (n=34) and exon 20 (n=54). Pt numbers were low, and wide 95% CIs were observed in groups with alterations not detectable by PCR (n=13) and in pts with multiple alterations. Some limitations of this retrospective plasma analysis include that this is a subgroup (66.6%) of the SOLAR-1 pt population and that the subgroup of pts with non-altered PIK3CA included pts with a PIK3CA mutation in their tumor tissue. Conclusions: ALP plus FUL demonstrated clinical benefit in pts with PIK3CA mutations detected in plasma ctDNA by NGS, in pts with single alterations, and in pts with alterations in exons 9 and 20. Results were consistent across pt groups, except in those with alterations not detectable by PCR. In conclusion, these data demonstrate a consistent clinical benefit of ALP plus FUL in various groups of pts with PIK3CA alterations detected in ctDNA by NGS. Clinical Outcomes of Patients With PIK3CA Alterations Detected in Plasma ctDNA by NGS in SOLAR-1Alpelisib + fulvestrantPlacebo + fulvestrantHR (95% CI)Events/N (%)mPFS, mo (95% CI)Events/N(%)mPFS, mo (95% CI)PIK3CA altered vs non-alteredAltered58/101(57.4)11.04(7.72-16.16)73/92(79.3)3.65(2.86-6.80)0.47(0.33-0.67)Non-altered40/87(46.0)10.87(5.59-16.76)60/101(59.4)5.45(3.75-9.00)0.60(0.40-0.91)PIK3CA: alteration detectable by PCR vs alteration not detectable by PCRDetectable52/88(59.1)12.48(7.36-18.37)66/80(82.5)3.58(2.37-5.65)0.44(0.30-0.64)Not detectable6/13(46.2)8.48(2.69-NA)7/12(58.3)7.39(1.87-12.98)1.12(0.35-3.56)PIK3CA: number of alterationsSingle45/83(54.2)12.88(7.36-18.50)50/64(78.1)3.58(1.87-6.11)0.43(0.28-0.65)Multiple13/18(72.2)9.00(3.68-18.37)23/28(82.1)4.63(3.48-9.63)0.55(0.25-1.20)PIK3CA alterations in exon 9 or exon 20Exon 918/34(52.9)15.21(7.03-NA)29/36(80.6)3.66(2.86-7.36)0.31(0.16-0.61)Exon 2034/54(63.0)10.91(5.72-18.37)40/48(83.3)3.52(1.87-6.11)0.51(0.31-0.82)CI, confidence interval; ctDNA, circulating tumor DNA; HR, hazard ratio; mPFS, median progression-free survival; mo, months; NA, not available; NGS, next-generation sequencing. Citation Format: Eva M. Ciruelos, Sibylle Loibl, Ingrid A. Mayer, Mario Campone, Hope S. Rugo, Monica Arnedos, Hiroji Iwata, Pier Franco Conte, Fabrice André, Albert Reising, Chong Ma, Michelle Miller, Naveen Babbar, Dejan Juric. Clinical outcomes of alpelisib plus fulvestrant in hormone receptor-positive, human epidermal growth factor receptor-2-negative advanced breast cancer with PIK3CA alterations detected in plasma ctDNA by next-generation sequencing: Biomarker analysis from the SOLAR-1 study [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD2-06.

Abstract PD2-07: Alpelisib + letrozole in patients with PIK3CA-mutated, hormone-receptor positive (HR+), human epidermal growth factor receptor-2-negative (HER2-) advanced breast cancer (ABC) previously treated with a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) + fulvestrant: BYLieve study results

Abstract Introduction: Mutations in PIK3CA, which encodes the α-isoform of phosphatidylinositol 3-kinase (PI3Kα), occur in ~40% of patients (pts) with HR+, HER2- ABC and can contribute to endocrine resistance. Alpelisib (ALP), a PI3Kα-selective inhibitor and degrader, plus fulvestrant (FUL) demonstrated efficacy in the phase 3 SOLAR-1 trial, which included 20 pts who had prior CDK4/6i in the PIK3CA-mutant cohort. Limited clinical data are available in the post-CDK4/6i setting for PIK3CA-mutated, HR+, HER2- ABC. BYLieve (NCT03056755), an ongoing phase 2, multicenter, open-label, 3-cohort noncomparative study, is the first trial evaluating ALP + endocrine therapy (FUL or letrozole [LET]) in pts with PIK3CA-mutated, HR+, HER2- ABC who progressed on/after prior therapy, including CDK4/6i. In the prior CDK4/6i + aromatase inhibitor (AI) cohort (Cohort A), pts received ALP + FUL. With median follow-up of 11.7 months (mo), the primary endpoint in Cohort A was met—50.4% of pts were alive and without disease progression (PD) at 6 mo per local investigator assessment (n=61; 95% CI, 41.2%-59.6%). Median progression-free survival (mPFS) was 7.3 mo (n=72; 95% CI, 5.6-8.3 mo); AEs were consistent with prior observations. Now, we report on the cohort of pts who received a CDK4/6i + FUL as immediate prior therapy before enrollment (Cohort B). Methods: Daily oral treatment in Cohort B consisted of ALP 300 mg + LET 2.5 mg. Each cohort planned to enroll at least 112 pts with centrally confirmed PIK3CA mutation, based on immediate prior treatment of either a CDK4/6i + AI (Cohort A), a CDK4/6i + FUL (Cohort B), or systemic chemotherapy or endocrine therapy (which may also include prior CDK4/6i + FUL; Cohort C, follow-up ongoing). The primary endpoint, the proportion of pts with centrally confirmed PIK3CA mutation alive without PD at 6 mo per local investigator using Response Evaluation Criteria in Solid Tumors (RECIST) 1.1, is assessed for each cohort separately and is met if the lower bound of the 95% CI is &amp;gt;30%. Men and premenopausal women were allowed goserelin 3.6 mg subcutaneously or leuprolide 7.5 mg intramuscularly every 28 days. Results: 126 pts whose immediate prior treatment was CDK4/6i + FUL were enrolled into Cohort B: 115 had centrally confirmed PIK3CA mutations. Median follow-up was 15.0 mo (range, 1-31 mo); 58 (46.0%) had ≥2 lines of prior therapy in the metastatic setting, and 103 (81.7%) pts progressed on prior AI therapy. The primary endpoint was met with 46.1% (95% CI, 36.8%-55.6%) of pts alive without PD at 6 mo. mPFS was 5.7 mo (95% CI, 4.5-7.2 mo). The most frequent all-grade AEs (≥25%) were diarrhea (67.5%), hyperglycemia (63.5%), nausea (54.8%), decreased appetite (44.4%), stomatitis (34.1%), fatigue (31.0%), rash (31.0%), and vomiting (24.6%). Most frequent grade ≥3 AEs included hyperglycemia (25.4%), rash (9.5%), and rash maculopapular (7.9%). Incidence of AEs leading to treatment discontinuation was 14.3% (n=18); most frequent AEs leading to discontinuation were rash (4 pts, 3.2%, including rash maculopapular), fatigue, and diarrhea (3 pts, 2.4% each). Conclusion: Alpelisib in combination with LET following progression on FUL + CDK4/6i and prior AIs was effective in this noncomparative trial. Consistent with the known safety profile of alpelisib, manageable toxicities were observed. These data suggest that alpelisib in combination with LET may be an effective treatment option for pts with PIK3CA-mutated, HR+, HER2- ABC in the post-CDK4/6i setting. Citation Format: Hope S. Rugo, Florence Lerebours, Dejan Juric, Nicholas Turner, Stephen Chia, Pamela Drullinsky, Aleix Prat, Rafael Villanueva Vázquez, Murat Akdere, Christina Arce, Yu-Ming Shen, Eva Ciruelos. Alpelisib + letrozole in patients with PIK3CA-mutated, hormone-receptor positive (HR+), human epidermal growth factor receptor-2-negative (HER2-) advanced breast cancer (ABC) previously treated with a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) + fulvestrant: BYLieve study results [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD2-07.

Breast cancer index (BCI) predicts benefit of two-and-a-half versus five years of extended endocrine therapy in HR+ breast cancer patients treated in the ideal trial.

512 Background: For postmenopausal women with hormone receptor positive (HR+) breast cancer, the optimal duration of extended endocrine therapy (EET), after completing 5 years of initial aromatase inhibitor (AI)–based adjuvant therapy, remains unclear. BCI [HOXB13/IL17BR (H/I)] is a gene expression-based biomarker that has been demonstrated to predict EET benefit in the MA.17 and Trans-aTTom studies in patients treated with adjuvant tamoxifen. The current study examined the ability of BCI (H/I) to predict endocrine benefit from 2.5 vs. 5 years of extended letrozole in the IDEAL trial. Methods: All patients with available tumor specimens were eligible for this blinded prospective-retrospective study. The primary endpoint was Recurrence-Free Interval (RFI). Median follow-up was 9.1 years from randomization. Kaplan-Meier and Cox proportional hazards regression analysis were used to analyze the differential benefit of EET with statistical significance of the interaction between BCI (H/I) and treatment assessed by likelihood ratio test. Results: 908 HR+ patients (73% pN+, median 59y, 45% pT1, 48% pT2, disease free at 2.5 years) were included, with 88% and 68% receiving prior treatment with an AI or chemotherapy, respectively. BCI by H/I status (High vs. Low) was significantly predictive of response from extended letrozole in the overall (N = 908) and pN+ (N = 664) cohorts. Notably, BCI (H/I) predicted EET benefit in patients that received any primary adjuvant therapy with an AI (N = 794). Treatment to biomarker interaction was significant in the overall (p = 0.045), pN+ (p = 0.029) and any prior AI (p = 0.025) cohorts, adjusted for age, pT stage, grade, nodal status, prior endocrine therapy and prior chemotherapy. Conclusions: Novel findings from this study demonstrate that BCI predicts endocrine benefit from extended letrozole in postmenopausal patients treated with primary adjuvant AI. These results support the growing body of evidence that BCI by H/I status predicts preferential endocrine response in distinct subgroups of patients, and further support its role as an important genomic tool to inform the risk-benefit regarding duration of extended endocrine therapy. Clinical trial information: NTR3077, BOOG 2006-05, Eudra-CT 2006-003958-16 . [Table: see text]

Prognostic and predictive value of ESR1 mutations in postmenopausal metastatic breast cancer (MBC) patients (pts) resistant to aromatase inhibitors (AI), treated with palbociclib (PAL) in combination with endocrine therapy (ET) or capecitabine (CAP) in the PEARL study.

1022 Background: Prior retrospective data has shown ESR1 mutation is an acquired resistant mechanism to AI. However, little is known about ist prognostic and predictive value to endocrine-based therapy and chemotherapy. PEARL study compared PAL+ET vs CAP in AI resistant patients. Here we wxplored prospectively the ESR1 mutational status based on updated PFS and OS. Methods: PEARL is a phase 3 study with 2 subsequent cohorts: cohort 1 with 296 pts randomized to PAL+Exemestane (EXE) vs CAP and cohort 2 with 305 pts randomized to PAL+ Fulvestran (FUL) vs CAP. ESR1 hotspot mutations were analyzed in circulating free DNA at baseline by digital PCR. Cox regresion analysis for PFS and OS were performed. Adjusted hazard ratios (aHR) and interaction test between treatment and ESR1 status were calculated. Results: ESR1 mutational status was assessed in 557 pts, 91% and 94% treated with CAP and PAL+ET, respectively; 164 (29%) had ESR1 mutations. Characteristics between ESR1 wild-type (WT) and mutated pts were balanced except for ECOG, prior sensitivity to ET, treatment line, prior AI for metastatic disease and time from first metastatic diagnosis to randomization. Median follow-up was 22.5 months (m). Median PFS was 9.6 vs. 7.5 m (HR: 1.06 [0.88 - 1.28], p = 0.522) and median OS was 30.2 vs 30.3 (HR: 0.99 [0.78 - 1.26] p = 0.934), for CAP vs. PAL+ET, respectively. No interaction was seen between treatment arm and ESR1 status either for PFS (p = 0.538) or OS (p = 0.957). Conclusions: In luminal MBC, ESR1-mutated pts had poorer OS than ESR1-WT pts regardless of treatment received. Clinical trial information: NCT02028507 . [Table: see text]

Abstract P1-19-04: Results from plasmaMATCH trial treatment cohort A: A phase II trial of extended-dose fulvestrant in patients with an ESR1 mutation identified via ctDNA screening (CRUK/15/010)

Abstract Background: Ligand binding domain ESR1 mutations are acquired in ER positive cancers during prior aromatase inhibitor therapy for advanced ER positive breast cancer (BC). ESR1 mutant cancer models are sensitive to fulvestrant at high concentrations, however standard dose fulvestrant may not achieve the concentration required to fully inhibit mutant ESR1 in the clinic. The plasmaMATCH trial Cohort A assessed the efficacy of extended-dose fulvestrant (double the current standard dose achieved by doubling the frequency of administration) in patients with an ESR1 mutation identified via ctDNA testing. Methods: The plasmaMATCH trial was an open-label, multi-centre, multi-cohort platform trial, consisting of ctDNA testing in ~1000 patients with advanced BC. Patients with an ESR1 mutation identified in ctDNA testing were potentially eligible to enter Cohort A. Patients were treated with fulvestrant 500mg intramuscularly on Cycle 1 Days 1, 8 and 15 of a 28 day cycle, and from Cycle 2 onwards every 15 days. Pharmacokinetics samples were collected pre-dose on Day 1 of Cycles 2, 3 and 4. The primary endpoint for Cohort A was confirmed objective response rate as defined by RECIST v1.1. The original planned sample size was 40 patients, to detect a 25% response rate, assuming predominantly clonally dominant mutations. As the trial progressed it became apparent that ctDNA screening may also detect sub clonal ESR1 mutations, which were expected to have a lower response rate. Using a single-stage A’Hern design with a target response rate of 20%, unacceptable response rate of 10%, alpha=5%, power=80, the sample size was increased to 78 evaluable patients with 13 or more responses required to infer efficacy. Results: Following ctDNA testing, 84 patients enrolled in Cohort A (38% of patients with ESR1 mutations identified in ctDNA testing). All were ER positive, seven were HER2 amplified, 78 (93%) had visceral metastases. The most common ESR1 mutations detected in baseline plasma were D538G (52.4%), Y537S (35.7%), E380Q (33.3%). In the 74 evaluable patients, confirmed response rate was 8.1% (95%CI 3.0-16.8%, 6/74). One additional patient had an unconfirmed partial response. Median progression free survival was 2.2 months (IQR 1.7-5.3 months) and median duration of response was 7.0 months (IQR 3.7-8.3 months) with 4 patients continuing on treatment. In exploratory analysis, 39 patients had clonally dominant ESR1 mutations in baseline ctDNA analysis whilst 25 patients had subclonal mutations and 10 had unknown clonality. The response rate in those with clonally dominant ESR1 mutations was 10% (95%CI: 2.9-24.2%, 4/39) with no confirmed responses in those with subclonal mutations. The most common clinically significant grade 3 or 4 adverse event was hypertension (13%). Pharmacokinetic analysis was consistent with elevated fulvestrant exposure compared to approved 500mg PopPk model (pre-dose Cycle 3, 71% increase, and pre-dose Cycle 4 66% increase). Conclusion: In the pre-treated population studied, the response rate of extended-dose fulvestrant did not meet pre-specified criteria for efficacy in patients with ESR1 mutations identified in ctDNA testing. Extended-dose fulvestrant was well tolerated and enhanced exposure was observed. Assessment of clonal dominance of ESR1 mutations in ctDNA may identify patients who are more likely to benefit from extended-dose fulvestrant therapy. Citation Format: Iain Macpherson, Lucy Kilburn, Sarah Kernaghan, Andrew M Wardley, Richard D Baird, Rebecca Roylance, Peter Stephens, Olga Oikonomidou, Jeremy P Braybrooke, Mark Tuthill, Jacinta Abraham, Matthew C Winter, Belinda Kingston, Katie Wilkinson, Alistair Ring, Judith M Bliss, Nicholas Turner, on behalf of the plasmaMATCH Trial Management Group. Results from plasmaMATCH trial treatment cohort A: A phase II trial of extended-dose fulvestrant in patients with an ESR1 mutation identified via ctDNA screening (CRUK/15/010) [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 P1-19-04.

High-Dose Toremifene as a Promising Candidate Therapy for Hormone Receptor-Positive Metastatic Breast Cancer with Secondary Resistance to Aromatase Inhibitors.

There are currently no established second- and later-line therapies for postmenopausal women with hormone receptor-positive advanced or metastatic breast cancer. We examined the efficacy of high-dose toremifene (HD-TOR) for this patient group and whether aromatase inhibitor (AI) resistance influences HD-TOR treatment outcome. This retrospective analysis investigated the outcomes of 19 women with postmenopausal hormone-sensitive recurrent or metastatic breast cancer who received HD-TOR, defined as 120 mg daily from 2012 to 2016. The median follow-up duration was 9.67 months. The overall response rate (ORR) and clinical benefit rate (CBR) were compared between various clinical subgroups, including patients exhibiting primary or secondary AI resistance as defined by the timing of recurrence or progression. Time to treatment failure (TTF) was estimated by the Kaplan–Meier method and compared between subgroups by the log-rank test. The overall ORR was 21.1%, and the CBR was 31.6%. CBR was significantly higher for patients without liver metastasis (50% vs. 0%, p = 0.044). Nine cases exhibited primary and eight cases secondary AI resistance. Both ORR and CBR were higher in patients with secondary AI resistance (25% vs. 0%, p = 0.087; 38% vs. 11%, p = 0.29). The median TTF was 6.2 months in the entire AI-resistant group (n = 17) and was longer in the secondary resistance subgroup than in the primary resistance subgroup (8.40 vs. 4.87 months; log-rank: p = 0.159). High-dose TOR appears to be most effective for postmenopausal breast cancer cases with secondary resistance to AIs, cases without prior AI treatment, and cases without liver metastasis. The detailed mechanisms of AI resistance and the clinical features of responsive cases need to be further clarified to identify the best candidates for HD-TOR.

Randomized phase-II evaluation of letrozole plus dasatinib in hormone receptor positive metastatic breast cancer patients

The non-receptor tyrosine kinase Src activation plays a role in the malignant progression of breast cancer, including development of endocrine therapy resistance and survival of bone metastases. This study investigated whether adding Src kinase inhibitor dasatinib to aromatase inhibitor (AI) therapy improved outcomes in estrogen receptor (ER)-positive, HER2-negative metastatic breast cancer (MBC). Postmenopausal patients with ER-positive, HER2-negative MBC (0–1 prior chemotherapies and no prior AI for MBC) were eligible for this non-comparative, parallel group, phase-II study. Patients were randomized to letrozole (2.5 mg/day PO) alone or with dasatinib (100 mg/day PO). Patients with disease progression on letrozole alone could crossover to dasatinib plus continued letrozole. The primary endpoint was clinical-benefit-rate (CBR; complete response + partial response + stable disease ≥6 months). A total of 120 patients were randomized. The CBR of 71% (95% CI 58–83%) was observed with letrozole + dasatinib versus the projected CBR of the combination of 56%. The CBR of 66% (95% CI 52–77%) with letrozole alone also exceeded the projected CBR of 39% with letrozole alone. The CBR was 23% in the crossover arm of letrozole plus dasatinib in patients progressing on letrozole alone. Median progression-free survival with the combination was 20.1 months and 9.9 months with letrozole alone. Letrozole plus dasatinib was well tolerated, although 26% of patients required dasatinib dose reductions. In this non-comparative phase-II trial, the CBR of 71% and the median PFS of 20.1 months with letrozole + dasatinib are encouraging and suggest that dasatinib may inhibit the emergence of acquired resistance to AI therapy.

Alpelisib (ALP)+fulvestrant (FUL) in patients from Japan with advanced breast cancer: Subgroup analysis of SOLAR-1 trial

Abstract Background Hyperactivation of PI3K pathway can occur due to PIK3CA mutations, which is present in ∼40% of patients (pts) with HR+, HER2- ABC. In SOLAR-1 (NCT02437318) trial, ALP+FUL significantly extended progression-free survival (PFS) vs placebo (PBO)+FUL in the PIK3CA-mutant (mut) cohort (median 11.0 vs 5.7 months; HR = 0.65; P Methods Men and postmenopausal women with HR+, HER2- ABC and recurrence/progression on/after prior aromatase inhibitor were randomized (1:1) to ALP (300 mg/day)+FUL (500 mg every 28 days+Cycle 1 Day 15) or PBO+FUL. This trial consisted of the PIK3CA-mut cohort for confirmatory purpose and the PIK3CA non-mutant (non-mut) cohort for proof of concept purpose. Primary endpoint was locally assessed PFS in the PIK3CA-mut cohort. Safety was assessed in the total population. Results Among 572 pts, 68 pts were enrolled in Japan; 36 pts in the PIK3CA-mut cohort received ALP+FUL (n = 17) or PBO+FUL (n = 19), and 32 pts in the non-mut cohort received ALP+FUL (n = 15) or PBO+FUL (n = 17). In JPN pts, ALP+FUL did not improve PFS in the mut cohort (median 9.6 vs 9.2 months; HR = 0.78). Duration of ALP exposure was shorter (median 1.7 months in JPN vs 5.5 months in overall population). Most frequent all-grade adverse events (JPN vs overall population) were rash (75.0% vs 53.9%), hyperglycemia (68.8% vs 65.8%), gastrointestinal toxicities (65.6% vs 75.4%), hypersensitivity and anaphylactic reaction (25.0% vs 16.5%). Severe cutaneous reactions (i.e. Stevens-Johnson syndrome, erythema multiforme) were observed only in JPN pts (n = 4; 12.5%). Conclusions Among pts from Japan, ALP+FUL showed no clinically meaningful improvement in PFS for pts with PIK3CA mut status and ALP exposure was much shorter than of the overall population. The incidence of cutaneous reactions was higher in Japanese vs overall population.

PIPA: A phase Ib study of β-isoform sparing phosphatidylinositol 3-kinase (PI3K) inhibitor taselisib (T) plus palbociclib (P) and fulvestrant (FUL) in PIK3CA-mutant (mt) ER-positive and taselisib (T) plus palbociclib (P) in PIK3CA-mutant (mt) ER-negative advanced breast cancer.

1051 Background: PI3K and CDK4/6 inhibitors synergise in ER+ve and –ve PIK3CA-mt breast cancer (BC) models. Escalation phase of this study set recommended phase 2 dose (RP2D) at P 125mg on a 3/1 scheme plus T 2mg daily ( Lim, ASCO 2017). Here we present the results of expansion cohorts for PIK3CA-mt BC patients (pts). Methods: The primary objective was to assess the confirmed objective response rate (ORR) of the P + T + FUL triplet in pts with measurable PIK3CA-mt ER+ve HER2-ve advanced BC, with up to two prior lines of chemotherapy for advanced disease. PIK3CA mutation was assessed in tissue or plasma DNA analysis. Exploratory objectives included assessment of efficacy of P + T in a cohort of pts with PIK3CA-mt advanced ER-ve BC. Safety is reported overall for 44 patients including an additional cohort of 7 PIK3CA-unknown ER+ve BC pts treated with P + T + letrozole (LET). For the P + T + FUL triplet a Simon minmax design was used, with 6 responses in 25 patients required to declare efficacy. Results: We recruited 24 assessable patients with PIK3CA-mt ER+ve HER2-ve advanced BC, median age 57 (42-74), median 3 (1-9) prior therapy lines for advance disease, with 24 (100%) receiving prior endocrine therapy and 23 (96%) prior aromatase inhibitor. ORR was 33% (8/24, 95% CI 16-55%), with median progression free survival (PFS) 7.9m (95% CI 5.6-11.8). For the 11 assessable PIK3CA-mt ER-ve pts (8 HER2-ve, 3 HER2+ve) receiving P + T, ORR was 0% (0/11), clinical benefit rate (CBR) 27% (3/11) and median PFS 4.3m (95% CI 1.8-6.1). Most common AEs across all cohorts were neutropenia (80%), fatigue (50%), mucositis (50%) and thrombocytopenia (30%). Most common grade 3/4 AEs were neutropenia (57%) and rash (11%). Translational research is ongoing. Conclusions: The triplet of P + T + FUL has promising efficacy in pre-treated PIK3CA-mt ER+ve advanced BC. A subset of patients with PIK3CA-mt ER-ve advanced BC had clinical benefit from P + T. The combination of P + T +/- FUL/LET was well tolerated with anticipated AEs. Clinical trial information: NCT02389842.

Randomized trial of text messaging (TM) to reduce early discontinuation of aromatase inhibitor (AI) therapy in women with breast cancer: SWOG S1105.

6516 Background: Non-adherence to AI’s for breast cancer is common and increases risk of recurrence. Text messaging (TM) has been shown to increase adherence to medications for chronic conditions. We conducted a multicenter randomized trial to evaluate if TM reminders improve AI adherence. Methods: Patients taking an AI for ≥30 days and having ≥36 mos of planned therapy were eligible. Patients were randomly assigned 1:1 to receive either TM or NO-TM twice a week for 36 mos. Randomization was stratified by length of time on prior AI therapy ( &lt; 12 (64%) vs. 12-24 mos (36%)) and AI class (anastrozole, letrozole, exemestane). Content themes of the 36 TMs focused on overcoming barriers to adherence. Patients were assessed for discontinuation of AIs every 3 mos for 36 mos. The primary outcome was time to non-adherence, where non-adherence was defined as urine AI metabolite assay results satisfying the following: &lt; 10 [units], undetectable, or no submitted specimen. A stratified Log-rank test was conducted. Multiple sensitivity analyses were performed using Cox regression. Results: In total, 724 patients were registered between May, 2012 and September, 2013, among whom 696 (338/360 (93.9%) on TM and 338/364 (92.9%) on NO-TM) were eligible and adherent at baseline. Observed (time-independent) adherence at 36 mos was 55.4% for TM and 55.4% for NO-TM. The primary analysis showed no difference in time-to-adherence failure between patients on the TM and NO-TM arms (HR = 0.89, 95% CI:0.76,1.05 p = .18). An analysis of negative urine tests alone resulted in similar non-significant results. With missed appointments not counted as failures, time to self-reported discontinuation (89.6% vs. 89.7%; HR = 1.17, 95% CI:0.69-1.98, p = .57) and site reported discontinuation (78.1% vs. 81.1%; HR = 1.31, 95% CI:0.86-2.01, p = .21) were also similar between the 2 groups. Conclusions: As the first large long-term randomized trial of an intervention directed at improving AI adherence, we found high rates of AI discontinuation. Bi-weekly text reminders did not improve adherence to AIs compared to usual care. Improving long—term adherence will likely require sustained behavioral interventions and support. Clinical trial information: NCT01515800.