Phase III study of lapatinib (L) plus trastuzumab (T) and aromatase inhibitor (AI) vs T+AI vs L+AI in postmenopausal women (PMW) with HER2+, HR+ metastatic breast cancer (MBC): ALTERNATIVE.

Abstract

1004 Background: Combination ofHER2-targeted therapy+AI improved clinical benefit in patients (pts) with HER2+, HR+ MBC vs AI alone in two previous trials, median progression free survival (mPFS) 4.8 vs 2.4 mo (TAnDEM), and 8.2 vs 3.0 mo (EGF30008). Dual HER2 blockade enhances clinical benefit vs single HER2 blockade. This study evaluated the safety and efficacy of dual vs single HER2 blockade (L+T vs T/L)+AI in HER2+, HR+ MBC progressing on (neo)adjuvant/first-line T+chemotherapy (CT). HER2 and HR status were assessed for eligibility at local lab. Methods: PMW were randomized 1:1:1 to receive T (8mg/kg followed by 6mg/kg IV Q3W)+L (1000mg/d)+AI or T+AI or L (1500mg/d)+AI. AI was per investigator’s choice. Pts were excluded if they were intended for CT. The primary endpoint was to assess superiority of PFS with L+T vs T. Secondary endpoints included PFS (L vs T), overall survival (OS), overall response rate (ORR), and safety. Results: 369 pts were enrolled; current analysis included 355 pts (data cutoff, March 11, 2016); L+T (n = 120), T (n = 117) or L (n = 118). Final PFS data were analyzed after 137 events. Baseline characteristics were balanced across all treatment (tx) arms. The primary endpoint was met; superior PFS was observed with L+T vs T (mPFS, 11 vs 5.7 mo; HR = 0.62, 95% CI [0.45, 0.88], P= 0.0064). This benefit of L+T was consistent in key subgroups. mPFS with L vs T was 8.3 vs 5.7 mo (HR = 0.71, 95% CI [0.51, 0.98], P= 0.0361). ORR with L+T, T, and L was 32%, 14%, and 19% respectively. OS data are immature. Most common adverse events (AEs) with L+T, T and L (≥15%, any arm) were diarrhea (69%, 9%, 51%), rash (36%, 2%, 28%), nausea (22%, 9%, 22%), and paronychia (30%, 0, 15%). Hepatic abnormalities of > 3 ULN ALT/AST levels were noted in 4%, 6%, and 16% respectively. Incidence of tx-related SAEs was 5%, 2%, and 4% and on-tx deaths was 3%, 4%, and 5%, respectively. Conclusions: Dual HER2 blockade with L+T+AI showed superior PFS benefit vs T+AI, in pts with HER2+, HR+ MBC. Incidence of AEs was increased with L+T. This combination can potentially offer an effective CT-sparing tx option in subgroup of HER2+, HR+ pts without aggressive disease and who are not candidates for CT. Clinical trial information: 2010-019577-16.