Timing of initiation of neratinib after trastuzumab-based adjuvant therapy in early-stage HER2+ hormone receptor (HR)-negative breast cancer: Exploratory analyses from the phase III ExteNET trial.

549Background: ExteNET, an international, randomized, placebo-controlled phase III trial, showed that neratinib given for 1 year after trastuzumab-based adjuvant 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. 2016; Martin et al. 2017]. Prespecified subgroup analyses showed greater benefit with neratinib in HR+ than HR tumors, and in patients who initiated neratinib ≤12 months of completing trastuzumab. To better understand the effects of neratinib in patients with HR disease, we examined the impact on efficacy of the interval from prior trastuzumab to start of neratinib in the HR subpopulation. Methods: Patients with early-stage HER2+ breast cancer received oral neratinib 240 mg/day or placebo for 1 year after standard trastuzumab-based (neo)adjuvant therapy. iDFS, the primary study endpoint, was examined in subgroups categorized according to the interval between completing trastuz...