Primary results from EMILIA, a phase III study of trastuzumab emtansine (T-DM1) versus capecitabine (X) and lapatinib (L) in HER2-positive locally advanced or metastatic breast cancer (MBC) previously treated with trastuzumab (T) and a taxane.

Abstract

LBA1 Background: T-DM1 is an antibody-drug conjugate comprising T, a stable linker, and the potent cytotoxic agent DM1; it incorporates the antitumor activities of T and the HER2-targeted delivery of DM1. Methods: EMILIA is a randomized study of T-DM1 vs XL, the only approved combination for T-refractory HER2+ MBC. Patients (pts) received T-DM1 (3.6 mg/kg IV q3w) or X (1000 mg/m2 PO bid, days 1–14 q3w) + L (1,250 mg PO daily) until progressive disease (PD) or unmanageable toxicity. Pts had confirmed HER2+ MBC (IHC3+ and/or FISH+), and prior therapy with T and a taxane. Primary end points were PFS by independent review, OS and safety. An interim OS analysis (efficacy boundary: HR= 0.617; p=0.0003) was planned at the time of the final PFS analysis. Results: 991 pts were enrolled; 978 received treatment. Median (med) durations of follow-up were 12.9 (T-DM1) and 12.4 (XL) months (mo). Baseline demographics, prior therapy and disease characteristics were balanced. There was a significant improvement in PFS favoring T-DM1 (med 9.6 vs 6.4 mo; HR=0.650 [95% CI, 0.549–0.771]; p <0.0001). The med T-DM1 OS was not reached vs 23.3 mo (HR=0.621 [95% CI, 0.475–0.813]; p=0.0005); the interim efficacy boundary was not crossed. T-DM1 was well tolerated with no unexpected safety signals. The most common grade ≥3 adverse events (AEs) per treatment were for T-DM1: thrombocytopenia (12.9% vs 0.2%), increased AST (4.3% vs 0.8%), and increased ALT (2.9% vs 1.4%); for XL: diarrhea (20.7% vs 1.6%), palmar plantar erythrodysesthesia (16.4% vs 0) and vomiting (4.5% vs 0.8%). The table lists other end points. Conclusions: T-DM1 conferred a significant and clinically meaningful improvement in PFS compared with XL. Other end points support T-DM1 as an active and well-tolerated novel therapy for HER2+ advanced BC. [Table: see text]