Abstract S5-02: Neratinib after trastuzumab-based adjuvant therapy in early-stage HER2+ breast cancer: 3-year analysis from a phase 3 randomized, placebo-controlled, double-blind trial (ExteNET)
Authors: Chan A , Delaloge S , Holmes FA , Moy B , Iwata H , Harker G , Masuda N , Neskovic Konstantinovic ZB , Petrakova K , Guerrero Zotano AL , Iannotti N , Rodriguez GI , Tassone P , von Minckwitz G , Ejlertsen B , Chia SKL , Mansi J , Barrios CH , Buyse M , Wong A , Bryce R , Ye Y , Martin M 
Published: May 2016

Background: Neratinib (Puma Biotechnology Inc), an irreversible pan-HER tyrosine kinase inhibitor, was evaluated in a phase 3 randomized, placebo-controlled, double-blind trial (ExteNET) to assess for improved invasive DFS (iDFS) in women with early-stage HER2+ breast cancer (BC) after trastuzumab-based therapy (clinicaltrials.gov NCT00878709). Primary efficacy analysis at 2-yrs demonstrated iDFS of 93.9% and 91.6% neratinib and placebo, respectively (HR 0.67, 95% CI 0.50–0.91; P=0.009). Greater benefit was observed in hormone-receptor (HR)-positive and centrally- confirmed HER2 subsets – HR 0.51, p=0.001 and HR 0.51 p=0.002, respectively [Chan et al. ASCO 2015]. We report an exploratory analysis of efficacy after 3-yrs of follow-up.

Methods: Women with HER2+ BC were randomly assigned to oral neratinib 240 mg/day or matching placebo for 1 year, stratified by nodal status, HR-status and prior trastuzumab regimen. The study was initiated in April 2009 with recruitment ceased in October 2011, limiting follow-up to 2 years. In January 2014, follow-up was restored to 5 years. During year 1, physical examinations were performed at 3-monthly intervals, at 4-monthly intervals in year 2 and then 6-monthly to 5-years; with mammography performed annually. Patients were asked to re-consent following ethics approval of the January 2014 protocol amendment. During years 3 to 5, disease-free survival (DFS) and survival events were identified from medical records. A descriptive analysis of iDFS, to investigate the durability of neratinib effect was performed after 3-yrs of follow-up. Data for overall survival remains blinded until 248 events have occurred. Hazard ratios (HR) with 95% confidence intervals (CI) were estimated using stratified Cox proportional-hazards models.

Results: The intention-to-treat population included 2840 patients (neratinib, N 1420; placebo, P=1420). Central HER2 testing has now been performed in 2041 pts (72%) - HER2-positive 1709 (84%) and HER2-negative 332 (16%). Pts were randomized within 12-months of completion of prior adjuvant trastuzumab in 2297 (81%) pts. Three-yr iDFS for ITT population demonstrated HR 0.74, [95% CI 0.56-0.96]. In the ITT pts who were randomized within 1-yr of trastuzumab completion, iDFS HR 0.72 [0.54-0.95]. For pts who had centrally-confirmed (cc) HER2-positive disease , iDFS HR 0.70 [0.50-0.98]. Pts with HR-positive disease had 3-yr iDFS HR 0.57 [0.39-0.82] and HR-negative pts HR 0.96 [0.67-1.45]. Overall survival data are not yet mature.

Conclusions: Exploratory analysis at 3-years supports the significant benefit seen in the primary analysis of 12-months of neratinib following adjuvant trastuzumab-based therapy. Patients who consistently derived the greatest benefit were 1) patients who received neratinib within 12 months of completing adjuvant trastuzumab; 2) centrally confirmed HER2 positive patients and 3) HR positive patients.

Citation Format: Chan A, Delaloge S, Holmes FA, Moy B, Iwata H, Harker G, Masuda N, Neskovic Konstantinovic ZB, Petrakova K, Guerrero Zotano AL, Iannotti N, Rodriguez GI, Tassone P, von Minckwitz G, Ejlertsen B, Chia SKL, Mansi J, Barrios CH, Buyse M, Wong A, Bryce R, Ye Y, Martin M. Neratinib after trastuzumab-based adjuvant therapy in early-stage HER2+ breast cancer: 3-year analysis from a phase 3 randomized, placebo-controlled, double-blind trial (ExteNET). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr S5-02.