Abstract
INTRODUCTION: CT-P6, the first trastuzumab biosimilar, was approved on the basis of data limited to human epidermal growth factor receptor-2 (HER2)-positive early breast cancer. Usage for other indications was granted by extrapolation, and post-approval clinical studies were conducted to confirm the effect of CT-P6 in HER2-positive gastric cancer. METHODS: After approval in Japan in 2018, a prospective post-marketing surveillance was conducted in 171 patients (130 male, 41 female) with HER2-positive unresectable advanced or recurrent gastric cancer. The safety and efficacy of CT-P6 were evaluated over 1 year. RESULTS: CT-P6 was primarily combined with fluoropyrimidine and/or platinum agents. Adverse events occurred in 151 patients (88.3%), with 55 patients (32.2%) experiencing grade 3 or higher. Infusion reactions occurred in 12.3%. Four cardiac disorders were reported: two of grade 1 cardiac dysfunction and two of severe ischemic heart disease. Interstitial lung disease was reported in four patients (2.3%). The objective response rate was 34.4%, and the disease control rate was 82.4%. The progression-free survival (PFS) was 7.4 months. Significant risk factors for PFS included gastroesophageal junction, ≥ 3 metastases, no gastrectomy, prior chemotherapy, and no platinum agent. CONCLUSIONS: In this cohort study, CT-P6 demonstrated sufficient efficacy and no new safety concerns in HER2-positive advanced gastric cancer, serving as a cost-effective alternative to originator trastuzumab. TRIAL REGISTRATION: Japan Registry of Clinical Trials, Trial ID: jRCT2071230094 (November 2023).