However, BILCAP is limited in its generalizability to an older adult population given that the median age in that study was 62 years (IQR, 55-69 years).10 Nevertheless, more recent data from the Japanese phase III Adjuvant S-1 vs Observation for Resected Biliary Tract Cancer (ASCOT) trial strengthen the case for the use of adjuvant fluorouracil for BTC.14 In ASCOT, 440 patients aged 20 to 80 years were randomized to adjuvant S-1, a mixture of tegafur (a fluorouracil prodrug), gimeracil (inhibitor of dihydropyrimidine dehydrogenase), and oteracil potassium or observation. The gene discussed is DPYD; the disease is biliary tract neoplasm.