(165/165 characters, including spaces): Pertuzumab, Trastuzumab, and an Aromatase Inhibitor for HER2-Positive and Hormone Receptor-Positive Metastatic/Locally Advanced Breast Cancer: PERTAIN Final Analysis

Purpose: In PERTAIN’s primary analysis (31 months’ median follow-up), adding pertuzumab to trastuzumab and an aromatase inhibitor (AI) with/without chemotherapy significantly improved progression-free survival (PFS) in patients with previously untreated HER2-positive and hormone receptor-positive metastatic/locally advanced breast cancer (M/LABC). A potentially enhanced treatment effect was observed in patients with no induction chemotherapy. We present the final analysis (>6 years’ median follow-up). Experimental Design: Patients (N = 258) were randomized 1:1 to pertuzumab (loading/maintenance: 840/420 mg) plus trastuzumab (loading/maintenance: 8/6 mg/kg) q3w and an AI (1 mg anastrozole or 2.5 mg letrozole daily) (Arm A), or trastuzumab and an AI (Arm B). Induction chemotherapy was at investigator discretion. Primary endpoint: PFS. Key secondary endpoints: overall survival (OS); safety. Results: Median PFS was 20.6 versus 15.8 months in Arms A and B, respectively (stratified HR, 0.67; P = 0.006). Median OS was 60.2 versus 57.2 months (stratified HR, 1.05; P = 0.78). Pertuzumab treatment effect was potentially enhanced in patients with no induction chemotherapy (26.6 versus 12.5 months). Any-grade adverse events (AEs) occurred in 122 patients per arm (96.1% versus 98.4%); grade ≥3 AEs in 72 (56.7%) and 51 (41.1%); serious AEs in 46 (36.2%) and 28 (22.6%). Conclusions: The PFS benefit of pertuzumab was maintained and OS was similar between arms at final analysis. Adding pertuzumab may enhance activity in patients who do not require first-line chemotherapy for M/LABC. No new safety concerns were reported. These data provide additional evidence of the role of first-line pertuzumab and trastuzumab in HER2-positive M/LABC.