Updated results of phase 1 study of DS-8201a in subjects with HER2-expressing gastric cancer.

118Background: DS-8201a is a HER2 targeting antibody-drug conjugate of high drug to antibody ratio (7 to 8) with a novel linker and topoisomerase I inhibitor. In preclinical studies, DS-8201a demonstrated a broad antitumor spectrum including efficacy against low HER2 expressing cancers. Interim results of the first-in-human phase 1 trial reported an overall confirmed response rate of 40.2% across several tumor types including breast and gastric (data cutoff of May 11, 2017). Here, we present updated results focusing on HER2 expressing gastric cancer (GC) subjects as of August 1, 2017. Methods: The trial consists of part 1, dose-escalation, and part 2, dose expansion cohorts. Part 2 included the cohort for subjects with HER2 expressing GC previously treated with trastuzumab. HER2 status was determined by IHC, and/or FISH according to ASCO CAP guidelines. Results: Seven GC subjects were enrolled in Part 1and 41 subjects were enrolled in Part 2. The median number of prior anticancer treatment was 3. In Part ...