Abstract P1-19-03: JAVELIN PARP Medley, a phase 1b/2 study of avelumab plus talazoparib: Results from advanced breast cancer cohorts

Background: Avelumab, a human IgG1 anti–PD-L1 monoclonal antibody, has shown antitumor activity and a manageable safety profile in several tumor types. Talazoparib, an orally available PARP inhibitor, is approved for the treatment of patients with deleterious or suspected deleterious germline BRCA1/2-mutated HER2− locally advanced (LA) or metastatic (M) breast cancer (BC). Preclinical data suggest that PARP inhibitors may have synergistic activity when administered in combination with immune checkpoint inhibitors. We report results from patients with LA/MBC enrolled in the phase 1b/2, multicohort JAVELIN PARP Medley study (NCT03330405). Methods: In phase 1b (cohort 1), patients with advanced solid tumors who had received ≥1 prior standard of care chemotherapy (CT) regimen were treated with avelumab 800 mg IV every 2 weeks (Q2W) in combination with talazoparib 1.0 mg orally once daily (QD) (dose de-escalation to 0.75 or 0.5 mg permitted following toxicity). In 2 phase 2 cohorts, eligible patients had either LA/M triple-negative BC (TNBC, cohort 2A) or LA/M hormone receptor positive (HR+), HER2−, DNA damage repair defect-positive BC (cohort 2B). Patients in cohort 2A had received 0 to 2 prior CT regimens (no progression on prior platinum-based CT) and patients in cohort 2B had received prior standard of care hormone therapy in either the adjuvant and/or LA/M setting followed by 0 to 2 prior CT regimens (no progression on prior platinum-based CT). The primary endpoint for phase 1b was first-cycle dose-limiting toxicities (DLTs) and for phase 2 was objective response (investigator assessed per RECIST v1.1). Adverse events (AEs) were characterized using National Cancer Institute Common Terminology Criteria for AEs v4.03. Results: By the data cutoff on December 24, 2018, 34 patients had been treated in cohorts 1 and 2. Twelve patients with advanced solid tumors were treated in cohort 1 (including 2 patients with TNBC); 3 patients (25.0%) had a first-cycle DLT: grade 3 neutropenia, (n=1) and grade 3 thrombocytopenia, (n=2). Best overall response (BOR) was partial response (PR) in 1 patient, stable disease (SD) in 3, progressive disease (PD) in 6, and non-complete response/non-PD in 1 patient with metastatic castration-resistant prostate cancer and non-measurable disease at baseline; 1 patient was not evaluable for response. Both patients with TNBC had a BOR of SD and remained on treatment for ≥9 months. Objective response rate in this pre-treated and heterogenous population was 8.3% (95% CI, 0.2, 38.5). Based on the phase 1b data, the recommended phase 2 dose was avelumab 800 mg Q2W and talazoparib 1 mg QD. By data cutoff, 22 patients had been treated in cohorts 2A (n=19) and 2B (n=3); median age was 56 and 50 years, respectively. In cohort 2A, 12 patients were evaluable for disease assessment; BOR was PR in 1, SD in 6, and PD in 5. All 3 patients in cohort 2B were non-evaluable for response at data cutoff. Treatment-related AEs (TRAEs) of any grade occurred in 11 patients (91.7%) in cohort 1, and 18 (94.7%) patients in cohort 2A. In cohort 2A, the most common TRAEs were anemia (57.9%), nausea (26.3%), fatigue (21.1%) and thrombocytopenia (21.1%); 9 patients (47.4%) had grade ≥3 TRAEs. There were no treatment-related deaths. Safety data from cohort 2B are not reported owing to low patient numbers. Observed pharmacokinetic (PK) data for avelumab 800 mg Q2W were similar to simulated data derived from a population PK model developed using 10 mg/kg dosing. Conclusions: Avelumab 800 mg Q2W administered in combination with talazoparib 1 mg QD in patients with advanced solid tumors, showed preliminary antitumor activity and a manageable safety profile, which was comparable to the safety profiles of the single agents. The study is ongoing; updated safety and efficacy data, and biomarker data will be presented. Citation Format: Timothy A Yap, Panagiotis Konstantinopoulos, Melinda L. Telli, Smita Saraykar, J Thaddeus Beck, Matthew D. Galsky, Jame Abraham, David R. Wise, Mustafa Khasraw, Gabor Rubovszky, Mikhail Dvorkin, Anil A Joy, Mateusz Opyrchal, Daria Stypinski, Colombe Chappey, Ross Stewart, Rossano Cesari, Anita Scheuber, Aditya Bardia. JAVELIN PARP Medley, a phase 1b/2 study of avelumab plus talazoparib: Results from advanced breast cancer cohorts [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 P1-19-03.