Five-Year Follow-Up of the Phase III ASCOT Trial of Adjuvant S-1 After Resection for Biliary Tract Cancer

The ASCOT phase III trial demonstrated that adjuvant S-1, an oral fluoropyrimidine, improved 3-year overall survival (OS) from 67.6% to 77.1% in patients with resected biliary tract cancer (BTC). We report the prespecified final 5-year follow-up analysis. In this multicenter, open-label, randomized trial conducted in Japan, 440 patients with resected BTC were assigned to observation (n = 222) or S-1 (n = 218). S-1 (40 mg/m ² twice daily, 4 weeks on/2 weeks off, for four cycles) was orally administered. The primary end point was OS in the intention-to-treat population. At a median follow-up of 61.5 months, the 5-year OS was 64% in the S-1 arm and 52% in the observation arm (hazard ratio [HR], 0.72 [95% CI, 0.55 to 0.95]; one-sided P = .01). The median OS was 8.2 years with S-1 and 5.9 years with observation. The median relapse-free survival was 3.5 versus 6.1 years (observation v S-1); unstratified and stratified (by primary tumor site and lymph node status) HRs were 0.80 (95% CI, 0.62 to 1.03) and 0.76 (95% CI, 0.59 to 0.98), respectively. Treatment effects were generally consistent across subgroups. These findings confirm a sustained survival benefit with adjuvant S-1 and support its role as a standard treatment for resected BTC.