Sex differences in the safety of S-1 plus oxaliplatin and S-1 plus cisplatin for patients with metastatic gastric cancer.

Previous studies have shown sex-related differences in the incidence of adverse events following treatment with fluoropyrimidines, however the mechanism of this difference is unknown. We examined sex-related differences in the safety of S-1 plus oxaliplatin (SOX) and S-1 plus cisplatin (CS) in 663 metastatic gastric cancer patients taking part in a phase III study. The incidences of leukopenia (odds ratio [OR] 1.9; P = .015), neutropenia (OR 2.2; P = .002), nausea (OR 2.0; P = .009), and vomiting (OR 2.8; P < .001) were increased in women versus men treated with SOX, while vomiting (OR 2.9; P < .001) and stomatitis (OR 1.8; P = .043) were increased in women versus men treated with CS. In contrast, male patients treated with CS experienced thrombocytopenia more often (OR 0.51; P = .009). The mean relative dose intensity of S-1 in SOX was 75.4% in women and 81.4% in men (P = .032). No difference in efficacy was observed between women and men undergoing either regimen. Sex-related differences in adverse reactions during SOX and CS treatment were confirmed in this phase III study. Further translational research studies are warranted to pursue the cause of this difference.