A Phase Ib/II Study of Cancer Stemness Inhibitor Napabucasin (BB608) Combined with Weekly Paclitaxel in Advanced Triple Negative Breast Cancer.

1094Background: Napabucasin (BBI-608, BB608) is a first-in-class cancer stemness inhibitor that targets the STAT3 pathway that has shown potent synergistic preclinical anti-tumor activity with paclitaxel. In a phase Ib dose escalation study in patients (pts) with advanced solid tumors, BB608 plus weekly paclitaxel was well tolerated. Methods: Pts with metastatic triple negative breast cancer (TNBC) who progressed on prior systemic therapy (including prior taxanes) were enrolled to assess safety, tolerability, and preliminary anti-cancer activity. BB608 was administered orally at 480 mg twice daily with paclitaxel 80 mg/m2 IV weekly 3 of every 4 weeks. A sample size of 40 set the bounds of the 90% CI at ±10% to 14%, assuming a disease control rate (DCR) of 60% to 80%. Disease control is defined as stable disease (SD) for at least 8 weeks, or objective partial (PR) or complete response (CR) per RECIST 1.1. Results: 35 pts enrolled, having received a median of 4 prior lines of therapy, including 33 pts (94%)...