A Phase 2 Study Of Napabucasin With Weekly Paclitaxel In Previously Treated Metastatic Breast Cancer.

1084Background: Napabucasin is a first-in-class cancer stemness inhibitor, identified by its ability to inhibit STAT3-driven gene transcription and spherogenesis of cancer stem cells (Li et al PNAS 112 (6):1839, 2015). Napabucasin has shown potent synergistic preclinical anti-tumor activity with paclitaxel (PTX). In a phase Ib dose escalation study in patients (pts) with advanced solid tumors, Napabucasin plus weekly paclitaxel was well tolerated. A phase II expansion cohort was opened for pts with previously treated metastatic breast cancer (MBC). Methods: Pts with metastatic MBC for whom weekly PTX was a reasonable treatment option received Napabucasin 240, 480, or 500 mg orally, twice daily in combination with paclitaxel 80 mg/m2 IV weekly on 3 of every 4 weeks. Adverse events were evaluated using CTCAE v4.03 and objective tumor assessments were obtained every 8 weeks per RECIST 1.1 criteria. Results: A total of 50 pts were enrolled including 34 with triple-negative disease (negative for estrogen recep...