Single agent activity of DS-8201a, a HER2-targeting antibody-drug conjugate, in heavily pretreated HER2 expressing solid tumors.

108Background: Human epidermal growth factor 2 (HER2) is a potential strong tumor driver for breast (BC) and gastric cancer (GC) as well as other HER2 expressing tumors. Antibody-drug conjugates (ADC) provide wider therapeutic window by more efficient and specific drug delivery. DS-8201a is a HER2 targeting ADC of high drug to antibody ratio (7 to 8) with a novel topoisomerase I inhibitor. In preclinical studies, DS-8201a showed a broader antitumor spectrum than T-DM1, including efficacy against low HER2 expressing tumors. Current trial includes dose escalation (Part 1) and expansion (Part 2) focusing on HER2 expressing solid tumors (NCT02564900). Methods: Part 1 used a modified continuous reassessment method to identify the expansion dose in patients (pts) with BC or GC. Part 2 was designed to evaluate the safety and efficacy in 4 expansion cohorts: T-DM1 treated HER2+ BC, trastuzumab treated HER2+ GC, BC with low HER2 expressing and other HER2 expressing solid tumors. Adverse events (AEs), objective res...