A multicenter phase II study of TAS-114 in combination with S-1 in patients with pretreated advanced gastric cancer (EPOC1604)

Background This is a phase 2 study aimed at evaluating the efficacy and safety of TAS-114, a novel deoxyuridine triphosphatase inhibitor, combined with S-1 in patients with advanced gastric cancer (AGC). Methods Eligible patients had AGC with measurable lesions, according to the Response Evaluation Criteria in Solid Tumors (RECIST, v1.1), with two or more previous chemotherapy regimens including fluoropyrimidines, platinum agents, and taxanes or irinotecan. The primary endpoint was objective response rate (ORR) according to the RECIST, v1.1. Twenty-nine patients were required according to Simon’s optimal two-stage design, with one-sided a = 5% and power = 80%. Threshold and expected ORRs were 5% and 25%. Patients received TAS-114 (400 mg/body, twice a day) and S-1 (30 mg/m 2 , twice a day) for 14 days, followed by 7 days of rest in one 3-week cycle. Protein expression levels of dUTPase and BRCA1 in tumor samples were determined by immunohistochemistry. Results Accrual was terminated in June 2018 because meeting the predefined efficacy criteria was considered difficult. ORR and disease control rate were 5.0% [95% confidence interval (CI), 0.1–24.9%] and 70.0% (95% CI, 45.7–88.1%), respectively, for all 20 patients enrolled. Median progression-free survival (PFS) and overall survival were 2.4 months (95% CI, 1.2–3.3 months) and 7.1 months (95% CI, 5.2–9.4 months), respectively. Median PFS in the groups with high and low dUTPase protein expression in the cytoplasm was 2.8 months (95% CI, 1.4–3.9) and 1.6 months (95% CI, 0.6–2.4), respectively [hazard ratio, 0.40 (95% CI, 0.16–1.04), log-rank test two-sided p = 0.047]. Grade 3 or higher treatment-related adverse events included anemia (20%), leucopenia (15%), neutropenia (10%), rash (10%), thrombocytopenia (5%), and lymphopenia (5%) Conclusions TAS-114 with S-1 showed only modest antitumor activity with acceptable safety profiles for patients heavily pretreated with AGC.