Correlation between relative dose intensity of adjuvant S-1 chemotherapy and psoas muscle mass volume and survival after resection of pancreatic ductal adenocarcinoma

Abstract Background This study aimed to investigate the prognostic relationship between relative dose intensity of adjuvant S-1 chemotherapy and psoas muscle mass volume in patients with resected pancreatic ductal adenocarcinoma. Methods We enrolled 105 patients with histologically confirmed pancreatic ductal adenocarcinoma who had undergone pancreatectomy. Results Adjuvant S-1 chemotherapy was administered to 72 (68.6%) of the 105 patients and not to the remaining 33 patients. Patients were stratified into high- and low-relative dose intensity groups by the cutoff value for relative dose intensity; the latter group included patients who did not receive adjuvant S-1 chemotherapy. Five-year overall and relapse-free survival rates were significantly higher in the high- than in the low-relative dose intensity group. There were statistically significant differences in 5-year overall and relapse-free survival between four patient groups stratified according to combinations of relative dose intensity and psoas muscle mass volume (5-year overall survival: P = 0.010, 5-year relapse-free survival: P = 0.044). The area under the curve for the combination of relative dose intensity and psoas muscle mass volume (0.694) was greater than that for relative dose intensity alone (0.657). According to multivariate analysis, a combination of relative dose intensity and psoas muscle mass volume was an independent prognostic factor in our study patients. Conclusions A sufficient dosage of adjuvant S-1 chemotherapy is important in improving survival of patients with resected pancreatic ductal adenocarcinoma. A combination of relative dose intensity and psoas muscle mass volume may predict the prognosis of patients with resected pancreatic ductal adenocarcinoma.