Randomized, optimal dose-finding, phase II study of tri-weekly nab-paclitaxel in patients with metastatic breast cancer (ABROAD)

1070 Background: Although nab-paclitaxel (nab-PTX) has shown superior efficacy compared to conventional paclitaxel in metastatic breast cancer (MBC), chemotherapy induced peripheral neuropathy (CIPN) was more frequently observed in nab-PTX. In a single arm Phase 2 trail (CA002-0LD), low dose nab-PTX (175mg/m2) every 3 weeks (q3w) demonstrated a good objective response rate (39.5%) without grade 3 or higher CIPN. Herein, we conducted multicenter randomized controlled study to evaluate optimal dose of nab-PTX comparing lower dose (LD or MD) to standard dose (SD). Methods: This study compared three different doses of q3w nab-PTX (SD: 260 mg/m2 vs. MD: 220 mg/m2 vs. LD: 180 mg/m2) in patients with HER2 negative metastatic breast cancer. Primary endpoint was progression-free survival (PFS). Grade 3/4 neuropathy rates in the three doses are estimated by the logistic regression. Optimal dose was selected by 2 step selection. At first, if hazard ratio (HR) for PFS was less than 0.75 or more than 1.33, the inferior dose was dropped. Then, if estimated incidence rate of grade 3/4 neurotoxicity exceed10%, that dose was also dropped. This trial is registered with the University Hospital Medical Information Network (UMIN), Japan (protocol ID C000012429). Results: In this study, 141 patients were randomly assigned to SD (n = 47), MD (n = 46) or LD (n = 48). Median PFS was 6.66 vs 7.34 vs 6.82 months, respectively. HR was 0.73 (95% confidence interval (CI): 0.42-1.28) in MD vs SD. SD was dropped due to inferiority to MD. HR was 0.77 (95%CI 0.47-1.28) in LD vs SD, and 0.96 (95%CI 0.56-1.66) in LD vs MD. LD and MD were carried over to next step due to equivalence. Overall survival was not different among all dose arms. Rate of dose reduction by treatment course was significantly higher in SD arm. Estimated incidence of grade 3/4 neurotoxicity rate was 29.5% in SD, 14.0% in MD and 5.9% in LD. Final selected dose was LD 180mg/m2. HR-QOL results will be presented. Conclusions: Low dose nab-PTX at 180 mg/m2/3 weeks could be an optimal dose with good clinical efficacy and tolerability for patients with MBC. Clinical trial information: C000012429.