Neratinib after adjuvant chemotherapy and trastuzumab in HER2-positive early breast cancer: Primary analysis at 2 years of a phase 3, randomized, placebo-controlled trial (ExteNET).

Abstract

508 Background: Neratinib (N) is an irreversible pan-HER tyrosine kinase inhibitor with clinical efficacy in trastuzumab (T) pre-treated HER2-positive (HER2+) metastatic breast cancer. In HER2+ early breast cancer (EBC), a significant proportion of patients (pts) recur with invasive disease despite T-containing adjuvant therapy. Methods: Women with stage 1–3c EBC with the last T dose ≤2y (later modified to stage 2–3c and ≤1y, respectively) and locally confirmed HER2+ were eligible. Pts were randomized to N 240mg PO once daily or placebo (P) for 12m, stratified by ER/PR, nodal status and T schedule. A global amendment reduced follow-up to 2y from study entry. A current amendment restores the original 5-y follow-up. Invasive DFS (IDFS) at 2y is the primary endpoint and other secondary endpoints include DFS + DCIS, distant DFS (DDFS), CNS incidence, and patient-reported outcomes. Overall survival (OS) is an event-driven secondary endpoint. Efficacy analyses were ITT using a stratified Cox model and log-rank test (1-sided α=0.025). Results: 2,821 pts were randomized between 07/2009 and 10/2011 (1,409 N; 1,412 P). Median time from last T was 4.4m N vs 4.7m P. Baseline characteristics were balanced between arms. Efficacy results are shown below. Pre-planned subset analyses showed a lower IDFS HR in ER/PR+ pts (n=1,616; HR=0.51 [0.33–0.77]) and in a centrally confirmed HER2+ cohort (HR=0.52 [0.34–0.79]). Diarrhea was the most common adverse event (AE) for N pts with 40% G3 (1pt G4). Other individual AEs ≥G3 occurred in < 4% N pts. Ejection fraction decrease ≥G2 was seen in 1.3% N vs 1.1% P pts. Mean relative dose intensity (RDI) was 88% in N vs 98% in P pts. Conclusions: ExteNET demonstrates that 12m of N following standard chemotherapy + T improves IDFS and DFS-DCIS at 2y in HER2+ EBC. Diarrhea, the most common AE, was manageable. Additional follow-up will allow assessment of 5-y IDFS and OS. ClinicalTrials.gov: NCT00878709. Clinical trial information: NCT00878709. Efficacy endpoint 2-y rate, % HR (95% CI) P-value (1-sided) stratified log rank N (n=1,409) P (n=1,412) IDFS 93.9 91.6 0.67 (0.50–0.91) 0.0046 DFS-DCIS 93.9 91.0 0.63 (0.46–0.84) 0.0009 DDFS 95.1 93.7 0.75 (0.53–1.05) 0.0447