Daiichi Sankyo Company, Limited announced that updated phase 1 safety and efficacy data for DS-8201, an investigational HER2-targeting antibody drug conjugate (ADC), in a subgroup of patients with HER2-expressing gastric cancer previously treated with trastuzumab and chemotherapy were presented during a poster session at the 2018 American Society of Clinical Oncology (ASCO) Gastrointestinal Cancers Symposium in San Francisco, California. Updated preliminary subgroup analysis results in 44 of 45 efficacy evaluable patients with HER2-expressing gastric cancer or gastroesophageal junction adenocarcinoma previously treated with trastuzumab and chemotherapy showed that DS-8201 demonstrated a confirmed overall response rate of 45.5% (20 of 44 patients) and a disease control rate of 81.8% (36 of 44 patients). Median duration of response was 7.0 months (95% CI: NR). The Kaplan-Meier estimate of median progression-free survival was 5.8 months (95% CI: 3.0, 8.3). A total of 17 out of 44 patients were continuing to receive treatment at the time of data cut-off. A subgroup analysis of 23 patients previously treated with CPT-11 (irinotecan) showed that DS-8201 demonstrated a confirmed overall response rate of 43.5% (10 of 23 patients) and a disease control rate of 82.6% (19 of 23 patients). Median duration of response was 6.9 months (95% CI: NR). The Kaplan-Meier estimate of median progression-free survival for this subgroup of patients was 4.1 months (95% CI: 2.5, 8.3). Updated preliminary safety data for this subgroup of trastuzumab-treated HER2-expressing gastric cancer patients were also reported. The most common adverse events (>30%, any grade) included nausea (71.1%), decreased appetite (64.4%), platelet count decreased (33.3%), white blood cell count decreased (33.3%) and constipation (31.1%). Grade 3 adverse events occurring in >10% of patients included anemia (24.4%), neutrophil count decreased (15.6%), platelet count decreased (13.3%) and white blood cell count decreased (11.1%). Grade 4 adverse events included platelet count decreased (4.4%), white blood cell count decreased (4.4%) and neutrophil count decreased (4.4%). Three patients discontinued treatment due to treatment-emergent adverse events (pneumonia, decreased appetite, and pneumonitis). Two potential cases of interstitial lung disease (ILD) were reported by the investigators (one grade 1 and one grade 3) in gastric cancer subjects and together with all reported or suspected ILD cases are being assessed by an independent ILD adjudication committee. These include two cases of potential Grade 5 pneumonitis previously reported in the breast cancer cohorts. Based on these phase 1 data, patients are currently being enrolled in the pivotal, phase 2 open-label DESTINY-Gastric01 study investigating the safety and efficacy of DS-8201 in patients with HER2-positive advanced gastric cancer or gastroesophageal junction adenocarcinoma (defined as IHC3+ or IHC2+/ISH+) who have progressed on two prior regimens including fluoropyrimidine agent, platinum agent and trastuzumab.