Biomarker Analysis of the Phase III NALA Study of Neratinib plus Capecitabine versus Lapatinib plus Capecitabine in Patients with Previously Treated Metastatic Breast Cancer

Purpose: Neratinib plus capecitabine (NthornC) demonstrated significant progression-free survival (PFS) benefit in NALA (NCT01808573), a randomized phase III trial comparing NthornC with lapatinib thorn capecitabine (L+C) in 621 patients with HER2-positive (HER2+) metastatic breast cancer (MBC) who had received >= 2 prior HER2-directed regimens in the metastatic setting. We evaluated correlations between exploratory biomarkers and PFS. Patients and Methods: Somatic mutations were evaluated by next-generation sequencing on primary or metastatic samples. HER2 protein expression was evaluated by central IHC, H-score, and VeraTag/HERmark. p95 expression (truncated HER2) was measured by VeraTag. HRs were estimated using unstratified Cox proportional hazards models. Results: Four hundred and twenty samples had successful sequencing: 34.0% had PIK3CA mutations and 5.5% had HER2 (ERBB2) mutations. In the combined patient populations, PIK3CA mutations trended toward shorter PFS [wild-type vs. mutant, HR = 0.81; 95% confidence interval (CI), 0.64-1.03], whereas HER2 mutations trended toward longer PFS [HR = 1.69 (95% CI, 0.97-3.29)]. Higher HER2 protein expression was associated with longer PFS [IHC 3+ vs. 2+, HR = 0.67 (0.54-0.82); H-score =240 versus