Lack of efficacy of adjuvant lapatinib in HER2-negative breast cancer (HER2–ve BC): Analysis of patients in the TEACH trial.

628 Background: Benefit from trastuzumab (T) in patients (pts) with HER2–ve tumors by central laboratory FISH testing was shown in an exploratory analysis of the NSABP B-31trial and confirmed by levels of expression of HER2 mRNA. DNA sequencing studies demonstrate that undetected HER2 mutations may drive tumor growth. It is hypothesized that pts with BC deemed as HER2–ve based on amplification may still benefit from anti-HER2 therapy. We undertook an exploratory analysis of disease free survival (DFS) in pts in TEACH whose tumors were HER2–ve or borderline by central FISH testing. Methods: TEACH, a randomized, double-blind, placebo (P)-controlled trial in 33 countries, evaluated lapatinib (L) in reducing relapse risk in T-naive pts pretreated with chemotherapy for HER2+ BC. L showed a hazard ratio (HR) for DFS compared with P of 0.83 (95% confidence interval [CI] 0.70-1.00); P=.053 in the ITT population (n=3147) and in pts with HER2+ BC by central FISH [HR: 0.82 (0.67-1.00); P=.04]. We conducted an explor...