Abstract PS11-28: Efficacy and safety of entrectinib in NTRK fusion-positive (NTRK-fp) breast cancer

Neurotrophic tyrosine receptor kinase genes (NTRK1/2/3) act as oncogenic drivers across a range of tumors. NTRK fusions occur at low frequency (90% of secretory breast carcinomas. Furthermore, up to 30% of patients (pts) with breast cancer will develop central nervous system (CNS) metastases (mets). Entrectinib is a potent, oral TRKA/B/C, ROS1 and ALK inhibitor, specifically selected for its CNS penetration properties. Entrectinib was evaluated in 3 global phase 1/2 clinical trials (ALKA-372-001 [EudraCT 2012-000148-88], STARTRK-1 [NCT02097810], and STARTRK-2 [NCT02568267]), where it demonstrated strong and durable systemic and intracranial efficacy in pts with NTRK-fp solid tumors, including those with breast cancer. We present updated data from this integrated analysis (data cut-off: 31 October 2018) focusing on pts with breast cancer. The entrectinib trials were conducted at >150 sites in 15 countries, and enrolled pts with locally advanced/metastatic NTRK-fp tumors (with or without baseline CNS mets) confirmed by nucleic acid-based methods. Tumor assessments were performed at the end of cycle 1 (4 weeks) and every 8 weeks thereafter, and evaluated by blinded independent central review (BICR) using RECIST v1.1. Primary endpoints were objective response rate (ORR) and duration of response (DoR) by BICR. Secondary endpoints included progression-free survival (PFS), overall survival (OS), and safety. At clinical cut-off, the overall efficacy-evaluable population included 74 adults from the 3 trials, with 12 different NTRK-fp tumor types and >25 histopathologies. In these pts, ORR by BICR was 63.5% (95% CI 51.5-74.4), including five complete responses (CR) and 42 partial responses (PR). Median (95% CI) DoR, PFS and OS were 12.9 (9.3-not estimable [NE]), 11.2 (8.0-15.7) and 23.9 (16.0-NE) months, respectively. The efficacy-evaluable NTRK-fp breast cancer cohort included 6 pts with a median age of 63 (range 36-67) years; most had an Eastern Cooperative Oncology Group performance status of 0 (3/6; 50%) or 1 (1/6; 17%). Breast cancer tumors were classified as secretory (4/6; 67%; all NTRK3-fp) or non-secretory (2/6; 33%; all NTRK1-fp). Pts had received 0 (3/6; 50%), 1 (1/6; 17%) or ≥4 (2/6; 33%) lines of prior therapy for metastatic disease. At data cut off, the median survival follow-up was 17.4 (range 1.7-23.9) months. ORR was 100% (2 CR, 2 PR; 95% CI 39.8-100.0) in pts with secretory and 50% (1 PR, 1 missing/unevaluable; 95% CI 1.3-98.7) in pts with non-secretory histology. Median (95% CI) DoR, PFS, and OS were 12.9 (4.2-NE), 10.1 (5.1-NE), and 23.9 (5.1-23.9) months, respectively. At baseline, 2 pts had CNS mets per investigator assessment; 1 of these pts had missing response data. CNS mets were confirmed by BICR in the other pt (non-secretory); this pt had received whole brain radiotherapy 2-6 months before starting entrectinib treatment, and had systemic PR and intracranial non-CR/non-progressive disease (non-measurable CNS lesion). The overall integrated safety-evaluable population comprised 504 pts with any gene fusion who received ≥1 dose of entrectinib. Most treatment-related adverse events (TRAEs) were Grade ≤3 (96.1%); the most frequently reported TRAEs were dysgeusia (39.7%) and fatigue (31.5%). Seven breast cancer pts were evaluated for safety, of whom six (85.7%) reported TRAEs; all were Grade ≤3. The most frequently reported TRAEs (each occurring in 3/7 pts; 42.9%) were nausea, anemia, and increased alanine or aspartate aminotransferase. Dose reductions and interruptions due to TRAEs were each reported in 3/7 pts (42.9%); no discontinuations or deaths due to TRAEs were recorded. In this updated integrated analysis, entrectinib induced objective responses in all pts with NTRK-fp breast cancer who had data available, and was generally well tolerated with no discontinuations due to TRAEs. Citation Format: Janice Lu, Collin M. Blakely, Christophe Le Tourneau, Saiama N. Waqar, Todd M. Bauer, Filippo de Braud, David S. Hong, Alexander Spira, Tira Tan, Samuel McCallum, Stuart Osborne, Brian Simmons, Minal Barve. Efficacy and safety of entrectinib in NTRK fusion-positive (NTRK-fp) breast cancer [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 PS11-28.