Phase Iii Study Of Lapatinib (L) Plus Trastuzumab (T) And Aromatase Inhibitor (Ai) Vs T Plus Ai Vs L Plus Ai In Postmenopausal Women (Pmw) With Her2+, Hr+ Metastatic Breast Cancer (Mbc): Alternative.

1004Background: 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, M...