Duration of extended adjuvant therapy with neratinib in early-stage HER2+ breast cancer after trastuzumab-based therapy: Exploratory analyses from the phase III ExteNET trial.

524Background: The optimal duration of adjuvant therapy with targeted agents remains a question of ongoing relevance in oncology. ExteNET, an international, randomized, placebo-controlled phase III trial, showed that neratinib given for 12 months after trastuzumab-based therapy significantly improved 2- (HR 0.67, p = 0.009) and 5-year (HR 0.73, p = 0.008) invasive disease-free survival (iDFS) in early-stage HER2+ breast cancer [Chan et al. Lancet Oncol 2016; Martin et al. Lancet Oncol 2017]. We examined the influence of duration of neratinib therapy on efficacy in the ExteNET study. Methods: Patients with early-stage HER2+ breast cancer were randomly assigned to oral neratinib 240 mg/day or placebo for 12 months (or until disease recurrence) after standard primary therapy and trastuzumab-based (neo)adjuvant therapy. Patients who received neratinib for ≤3 or ≥11 months (the median duration of neratinib treatment) were each compared with the ITT placebo group. iDFS (primary endpoint) was analyzed using Kapl...