Efficacy and Safety of Trastuzumab in Combination with S-1 and Cisplatin Therapy for Japanese Patients with HER2-Positive Advanced Gastric Cancer: Retrospective Analysis

: The combinations of oral fluoropyrimidines and cisplatin such as capecitabine and cisplatin (XP) or S-1 and cisplatin (SP) are regarded as a standard therapy against unresectable, recurrent, or advanced gastric cancer (AGC). Especially, SP is the most common regimen against AGC in Japan. For patients with human epidermal growth factor receptor type 2 (HER2)-positive AGC, trastuzumab, a monoclonal antibody targeting HER2 antibody, is additionally used in combination. Although trastuzumab in combination with XP (trastuzumab-XP) have been widely accepted, the efficacy of trastuzumab in combination with SP (trastuzumab-SP) lacks sufficient verification. The aim of the present study is to validate the comparability of trastuzumab-SP to trastuzumab-XP. Patients with HER2-positive AGC were assigned to the trastuzumab-XP or trastuzumab-SP group. We then retrospectively compared the efficacy and safety between both groups. As a first-line chemotherapy, trastuzumab in combination with XP or SP was administered to 58 patients: 28 with trastuzumab-XP and 30 with trastuzumab-SP. In the trastuzumab-XP group, response rate (RR), disease control rate (DCR), median progression-free survival (mPFS), and median overall survival (mOS) were 39.3%, 89.3%, 7.9 months, and 20.0 months, respectively. In the trastuzumab-SP group, RR, DCR, mPFS and mOS were 50.0%, 86.7%, 6.9 months, and 16.7 months, respectively. No significant difference in efficacy was observed between both groups. Severe hand-foot syndrome was observed more frequently in the trastuzumab-XP group than in the trastuzumab-SP group (14.3% vs. 0%, p = 0.05). Trastuzumab in combination with SP is a potential first-line therapeutic option for patients with HER2-positive AGC.