Prognosis following an extended duration of adjuvant gemcitabine plus S-1 chemotherapy in patients with pancreatic ductal adenocarcinoma: Analysis using inverse probability of treatment weighting.

BACKGROUND/PURPOSE: The aim of this study was to assess whether the duration of adjuvant gemcitabine plus S-1 (GS) chemotherapy has any effect on survival in patients with pancreatic ductal adenocarcinoma (PDAC). METHODS: Of the 290 patients who received adjuvant GS chemotherapy, 100 (34%) received the standard duration (20-29 weeks) and 190 (66%) received an extended duration (≥30 weeks). To reduce selection bias, the prognostic impact (recurrence-free survival [RFS] and overall survival [OS]) based on the duration of adjuvant GS chemotherapy was analyzed using inverse probability of treatment weighting (IPTW). Moreover, to reduce immortal time bias, time-dependent multivariate analyses in which implementation of adjuvant GS chemotherapy was treated as time-varying covariate was also performed. RESULTS: Extended duration of adjuvant GS chemotherapy was significantly correlated with prolonged RFS (P < .001) and OS (P < .001) after IPTW adjustment. Time-dependent multivariate analyses revealed that extended duration of adjuvant GS chemotherapy was an independent prognostic factor for prolonged RFS (hazard ratio [HR], 0.58, P = .002) and OS (HR, 0.56, P = .005). CONCLUSION: Extended duration (≥30 weeks) of adjuvant GS chemotherapy in patients with PDAC was associated with an improved prognosis. These findings warrant a further prospective trial on PDAC to investigate the survival benefit of extended adjuvant chemotherapy.