HALT MBC: HER2 suppression with the addition of lapatinib to trastuzumab in HER2-positive metastatic breast cancer (LPT112515).

Abstract

TPS658 Background: Dual blockade of HER2 with the combination of trastuzumab (T) and lapatinib (L) enhances antitumor activity in HER2-positive breast cancer (BC) preclinical models due to the complementary mechanisms of action of the 2 agents. In patients (pts) with T-treated HER2-positive metastatic BC (MBC), treatment with the combination was associated with longer progression-free (PFS) and overall survival (OS) compared with L alone. In pts with stage II/III BC, preoperative treatment with the combination plus paclitaxel (P) resulted in significantly higher pathologic complete response rates compared with P combined with either agent alone. This evidence supports the concept of dual HER2 blockade as a treatment strategy for HER2-positive MBC. The present study is designed to evaluate whether the addition of L improves PFS among women with HER2-positive MBC receiving T as maintenance therapy. Methods: In this open-label, Phase III study, 280 pts will be stratified by line of treatment (first/second) and hormone receptor status (positive/negative), then randomized 1:1 to receive maintenance treatment with either L (1000 mg qd, continuously) in combination with T (6 mg/kg once every 3 weeks [q3w]) or T (6 mg/kg q3w) alone. Pts will receive study treatment until disease progression, death, discontinuation due to adverse events, or other reasons. The primary endpoint is PFS; secondary endpoints are OS, clinical benefit rate, and safety. Key eligibility criteria include pts with HER2-positive MBC who have completed 12 to 24 weeks of first- or second-line treatment with T plus chemotherapy with an objective response or stable disease at time of chemotherapy discontinuation. Pts with stable brain metastases are eligible if entering the study on second-line treatment. Efficacy endpoints will be analyzed in the ITT population. A total of 193 PFS events is required to detect a 50% increase in median PFS (hazard ratio=0.67) for L plus T compared with T alone (median PFS 27 vs 18 weeks, respectively). The hypothesis will be tested using a 1-sided test with 80% power and a type I error of 0.025. The trial is currently open for accrual in the United States and Canada.