Trastuzumab emtansine (T-DM1) in patients (pts) with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC): Results from a multicenter retrospective analysis

Abstract

Background: T‐DM1 improved outcomes in pts with HER2+ MBC, but few data concerning its use in routine clinical practice are available. Methods: We retrospectively enrolled 194 HER2+ (IHC 3+ or 2+ amplified) MBC pts treated with T‐DM1 in real‐world practice in 20 Italian oncologic centers. Results: Baseline pts and tumors characteristics are listed in Tab 1. Median (m) follow up was 9.8 months (mo) (range,2‐37), m T‐DM1 treatment duration was 5 mo (range, 1‐30). Among 183 evaluable pts, 5.4% had a complete response and 35% a partial response, for an Overall Response Rate of 40% (95%CI, 33‐47). A stable disease (SD) was recorded in 26.8% pts, with a clinical benefit (CB: response or SD lasting > 6 mo) of 55% (95%CI, 47‐62). No significant differences in responses have emerged according to disease sites. M Progression Free Survival (PFS) was 6 mo (95%CI, 5‐7), m Overall Survival (OS) was 35 mo (95%CI, 11‐59). Pts who have previously carried out <3 lines for MBC had improved PFS (p = 0.006). At multivariate analysis, factors related to PFS benefit were lower ECOG performance status (PS) (p < 0.0001) and HER2+ status at first diagnosis (p = 0.03), while OS benefit was related with lower ECOG PS (p = 0.01), absence of brain metastases (p = 0.08), other than ductal histology (p = 0.04) and CB (p < 0.0001). Central nervous system (CNS) progression occurred in 10.4% of the pts without CNS metastases, and in 29.1% of the pts with CNS metastases at baseline. Pts with CNS metastases at baseline have a m PFS similar to that observed in the general population, whereas m OS was shorter (16 mo, C.I. 95%, 12‐21). Toxicity was manageable, with grade >3 adverse events reported in 5.6% of pts, most commonly thrombocytopenia and fatigue. Cardiac dysfunction was reported in 2 pts (1%). Conclusions: In this real‐world setting of heterogeneous HER2+ MBC pts, efficacy of T‐DM1 was comparable with that reported in phase II‐III studies, without new safety issues. (Table Presented).