MacroGenics, Inc. announced presentation of updated data from its Phase 2 clinical trial of margetuximab plus pembrolizumab for patients with advanced HER2+ gastric carcinoma in a poster session at the 2019 ASCO Gastrointestinal Cancers Symposium in San Francisco, California. The poster was titled "Antitumor Activity of Margetuximab plus Pembrolizumab in Patients with Advanced HER2+ (IHC3+) Gastric Carcinoma." This Phase 2 open-label, dose escalation study evaluates the combination of margetuximab, an investigational Fc-optimized anti-HER2 monoclonal antibody, with pembrolizumab, an anti-PD-1 antibody, a regimen that is designed to coordinately engage innate and adaptive immunity for the treatment of patients with gastroesophageal cancer. The trial seeks to characterize the safety, tolerability, maximum tolerated dose, and antitumor activity of this combination. Enrolled patients had relapsed or refractory advanced HER2+ gastric or gastroesophageal junction cancer with disease progression after or resistance to treatment with trastuzumab plus chemotherapy. The 25 patients in the most recently enrolled expansion cohort had HER2+ gastric carcinoma that was 3+ by immunohistochemistry (IHC). Patients in the study were enrolled irrespective of PD-L1 expression status. Acceptable tolerability was observed in the safety population of 95 patients, 92 of whom were treated at the recommended Phase 2 dose of 15 mg/kg for margetuximab and 200mg for pembrolizumab, both on an every three week schedule of administration. Grade 3 or higher treatment-related adverse events (TRAE) occurred in 17.9% of patients, the most common of which was infusion-related reaction (3.2%). As of the January 8, 2019 data cut-off date for the current update of this ongoing study, objective responses were observed in 18/55 HER2+ (IHC 3+) response-evaluable gastric cancer patients, including 14 confirmed and 4 unconfirmed. The Objective Response Rate (ORR) for this population was 32.7%, with a Disease Control Rate (or DCR, which includes partial responses and stable disease) of 69.1%. Median Progression-Free Survival (PFS) was 4.7 months. In the subset of these patients who were also PD-L1 positive, objective responses were observed in 12/23 (52.2%) patients, with a DCR of 82.6% and PFS of 4.14 months. As of the data cut-off date, the study was ongoing with 13 gastric cancer patients remaining on therapy. The median Overall Survival (OS) had not been reached in either of these groups.