Phase II randomized, open-label study of YM155 (sepantronium bromide) plus docetaxel versus docetaxel alone as first-line treatment for HER2 negative metastatic breast cancer.

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548 Background: YM155 (YM) is a small molecule survivin suppressant. In a phase I/II study of YM plus docetaxel (D) in solid tumors evidence of anti-tumor activity was observed in women with human epidermal growth factor 2 non-overexpressing (HER2 negative) metastatic breast cancer (mBC). Methods: This was a randomized study of YM plus D versus D as 1st line treatment in subjects with HER2 negative mBC. Eligibility criteria were: ECOG < 1, no prior chemotherapy for mBC, and at least one measurable lesion. Primary endpoint was progression free survival (PFS); secondary endpoints were: objective response rate (ORR), overall survival (OS), duration of response (DOR), clinical benefit rate (CBR), time to response (TTR) and safety. YM was administered at 5 mg/m2/day as a 168 hr continuous infusion followed by 14 Day (d) observation and D was administered at 75 mg/m2over 1 hr on d1 every 21d. In the control arm, D was dosed per investigator choice q 21d. Results: 101 subjects were randomized (50 YM + D; 51 D). Median (m) age 55 (range: 25 – 79), 25% had triple negative disease, > 60% had bone and lymph mets, 86% had prior therapy for BC. mPFS (days) was 251 (95%CI: 176 – 333) YM + D vs 252 (95%CI: 202-433) D (p=0.34). ORR, CBR and TTR (YM+D; D): 26% vs. 25.5%; 82% vs. 84.3% and 45 vs 59 d. OS data are immature but showed no difference (p=0.911). Adverse events [AEs (> 25%)] [YM + D% vs D %]: neutropenia 83 vs 84, alopecia 62.5 vs 53, fatigue 50 vs 41.2, nausea 35.4 vs 41.2, leucopenia 27 vs 33 and dyspnoea 33 vs 14. Common (>10%) serious AEs [YM + D% vs D%]: febrile neutropenia 21 vs 8 and neutropenia 10 vs 8. Conclusions: Preclinical and clinical evidence suggested the combination of YM + D may offer additional benefit to D alone in subjects with mBC. This study showed no difference in efficacy, but the combination appeared to be well tolerated. Clinical trial information: NCT01038804.