Safety and efficacy of the BCL2 inhibitor venetoclax in estrogen receptor (ER) and BCL2-positive metastatic breast cancer: The mBEP study.

Abstract

1044 Background: The anti-apoptotic protein BCL2 is overexpressed in ~85% of ER+ breast cancer (BC). Venetoclax (ABT-199), a BCL2 inhibitor approved for CLL (400 mg/day), synergizes with tamoxifen in preclinical patient derived xenograft models by increasing apoptosis. In the first study to evaluate venetoclax in solid tumors, we tested the safety and efficacy of this combination in ER+BCL2+ metastatic BC. Methods: A ‘3+3 design’ dose escalation phase 1b study enrolled women with ER+ ( > 1%), BCL2+ ( > 10%, mod-high) and HER2 non-amplified metastatic BC. Patients received escalating doses of venetoclax 200, 400, 600 or 800 mg/day with tamoxifen 20 mg/day. The primary objective was to determ..