Adjuvant S-1 After Biliary Tract Cancer Surgery (ASCOT Phase III): JCO | September 2026
What Did the Study Find?
The prespecified final analysis of the ASCOT phase III trial evaluated whether the survival benefit of adjuvant S-1 persists after curative resection of biliary tract cancer (BTC).
- 440 patients were randomized to adjuvant S-1 or observation after resection.
- At median 61.5 months follow-up, 5-year overall survival was 64% with S-1 vs 52% with observation.
- S-1 reduced the risk of death by 28% (HR 0.72).
- Median overall survival was 8.2 vs 5.9 years.
- Median relapse-free survival was 6.1 years with S-1 vs 3.5 years with observation.
- Treatment benefit was generally consistent across prespecified subgroups.
- These long-term results confirm that the earlier 3-year survival advantage was durable rather than transient.
Why Does It Matter?
Evidence for effective adjuvant therapy after BTC resection remains limited. ASCOT now provides mature randomized evidence demonstrating a sustained survival benefit.
GastroAGI Takeaway
ASCOT confirms adjuvant S-1 as a standard option after resection of biliary tract cancer in Japan. The clinically important finding is the durable 12-percentage-point absolute improvement in 5-year survival. However, because ASCOT was conducted entirely in Japan, generalizability and the choice between S-1 and other regionally established adjuvant regimens remain important considerations.
