A phase 2 study of napabucasin with weekly paclitaxel in previously treated metastatic breast cancer.

Abstract

1084 Background: 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 receptor [ER], progesterone receptor [PR], and Her2 and no prior history of positive receptor status). There were 9 pts positive for ER, PR, or Her2 and refractory to targeted agents, and 7 pts with conversion to triple-negative disease from pathology previously positive for ER, PR or Her2. Pts were heavily pre-treated, having received a median of 5 prior lines of systemic therapy. All but 3 patients had received previous systemic treatment with a taxane. Napabucasin + PTX was well tolerated. Grade 3 AE occurring in ≥ 5% patients was diarrhea (n = 4), and 1 pt had grade 4 diarrhea. The objective response rate (ORR), disease control rate (DCR), median progression free survival (mPFS), and median overall survival (mOS) for all pts and for each sub-group are summarized in the table. Conclusions: Napabucasin (BBI-608) plus weekly paclitaxel has demonstrated safety, tolerability, and encouraging signs of anti-cancer activity in pts with pretreated metastatic breast cancer. Further clinical evaluation of this combination regimen in controlled trials is warranted. Clinical trial information: NCT01325441. [Table: see text]