Clinical effects of prior trastuzumab on combination eribulin mesylate plus trastuzumab as first-line treatment for HER2+ locally recurrent or metastatic breast cancer (MBC): Results from a phase 2, single-arm, multicenter study.

Abstract

139 Background: Eribulin mesylate, a novel nontaxane microtubule dynamics inhibitor in the halichondrin class of antineoplastic drugs, is indicated for women with MBC who previously received ≥ 2 chemotherapy regimens in the metastatic setting. Primary data from a phase 2 trial on first-line combination eribulin + trastuzumab (TRAS) in HER2+ patients (pts) showed a 71% objective response rate (ORR) and tolerability consistent with the known profile of these agents. Here we present prespecified endpoint data for this study by prior TRAS use. Methods: Pts with HER2+ MBC who had not received prior chemotherapy for MBC received eribulin mesylate 1.4 mg/m2 IV on days 1 and 8 of each 21-day cycle and initial TRAS (8 mg/kg IV/day 1), followed by 6 mg/kg/day 1 of each subsequent cycle. Response, progression-free survival (PFS), and tolerability were assessed in patients who had and had not received prior TRAS treatment. Results: The 52 pts (median age, 59.5 years) received combination eribulin + TRAS, for a median treatment duration of ~30 weeks; 40% (n=21) were previously treated with TRAS in the neo-adjuvant/adjuvant setting. There was median of 23 months since completion of adjuvant treatment prior to retreatment with eribulin + TRAS for first-line MBC.Efficacy, assessed by ORR, clinical benefit rate (CBR), PFS, and duration of response (DOR), was largely consistent in pts who received prior TRAS relative to pts who had not received prior TRAS (see table). Overall, grade (G) 3-5 adverse events (AEs), treatment-related AEs (TRAEs), and discontinuations (d/c) were similar between groups (Table). Conclusions: In this phase 2 single-arm trial in pts with HER2+ MBC, eribulin + TRAS demonstrated activity and was well tolerated as first-line treatment, irrespective of prior (neo) adjuvant TRAS treatment. Clinical trial information: NCT01269346. [Table: see text]