Association between treatment duration and overall survival in early-stage HER2+ breast cancer patients receiving extended adjuvant therapy with neratinib in the ExteNET trial.

540 Background: Completion of planned treatment has been shown to improve clinical outcomes. In the ExteNET trial (NCT00878709), where diarrhea prophylaxis was not mandated, 17% of patients (pts) discontinued neratinib early due to diarrhea. This compares with 3.3% of pts from the CONTROL trial (NCT02400476) who used a neratinib dose-escalation strategy. Prior analyses have shown improved invasive disease-free survival (iDFS) in pts who completed planned duration of neratinib therapy in ExteNET (Table). Here we assess outcomes, including overall survival (OS), for pts who completed planned therapy in 3 groups from ExteNET: intent-to-treat (ITT) population; pts with hormone receptor-positive (HR+) disease who initiated neratinib within 1y after prior trastuzumab (HR+/≤1y, the population neratinib is approved for in the EU); and HR+/≤1y with residual disease post-neoadjuvant therapy (no pathologic complete response [pCR]). Methods: Pts with early-stage HER2+ breast cancer received oral neratinib 240 mg/d or placebo after trastuzumab-based (neo)adjuvant therapy. Pts who completed neratinib therapy (defined as ≥11m or cessation of neratinib if recurrence occurred prior to 11m) were compared with placebo (all randomized pts). iDFS and OS were analyzed using Kaplan-Meier methods; hazard ratios (HR) with 95% confidence intervals (CI) were estimated using Cox proportional-hazards models. Data cutoff: July 2019. Results: There were 2840 pts in the ITT population. The table shows iDFS and OS in the overall population and in pts who completed planned duration of neratinib therapy. Completion of planned neratinib was associated with improvements in iDFS and OS in all groups evaluated. Conclusions: These descriptive findings suggest that pts who receive the recommended duration of treatment of 1y with neratinib may have improved outcomes. Clinical trial information: NCT00878709. [Table: see text]