The impact of preoperative skeletal muscle loss on the completion of S-1 adjuvant chemotherapy for gastric cancer

Purpose Body weight loss after surgery for gastric cancer is related to S-1 compliance and it also affects the prognosis. However, it is unclear whether the preoperative skeletal muscle mass affects S-1 completion for gastric cancer. We investigated the impact of preoperative skeletal muscle mass loss on the completion of S-1 adjuvant chemotherapy for gastric cancer. Methods We retrospectively analyzed data from 53 patients who underwent curative gastrectomy followed by adjuvant S-1 monotherapy for pStage II-III gastric cancer between 2012 and 2021 at our hospital. The psoas muscle mass index (PMI) was used as the index for preoperative skeletal muscle mass. Results Thirty-six patients completed S-1 treatment and 17 discontinued treatment. The patients who completed S-1 treatment had a longer overall survival than those who discontinued treatment (log-rank test, p = 0.043). According to a univariate analysis, the patients in the discontinuation group had a significantly lower preoperative body mass index (< 22.9 kg/m(2), p = 0.005) and a higher rate of adverse events (grade 2 or higher, p < 0.001) than those in the completion group. According to a multivariate analysis, preoperative PMI (HR 3.563, p = 0.030) was an independent predictive factor for S-1 completion. Conclusion Preoperative skeletal muscle loss might therefore prevent the completion of adjuvant chemotherapy S-1 in patients with gastric cancer.