Raw research findings for this medication. Mostly single studies, not curated or confirmed robust.
S-1 is an oral chemotherapy combining tegafur, which the liver converts into fluorouracil; gimeracil, which blocks the enzyme that breaks fluorouracil down, keeping its levels up; and oteracil, which reduces fluorouracil's effects on the gut. It is widely used in Japan and East Asia for stomach, bowel, pancreatic and other cancers, and in Europe as Teysuno. It is also sold as TS-1.
CYP2A6 converts tegafur into fluorouracil, and its low-activity versions, common in East Asian populations, mean less conversion. Because gimeracil already blocks the DPYD enzyme, the effect of DPYD variants is thought to be smaller than with fluorouracil itself, though studies still looked at DPYD. Studies also looked at UGT1A genes for side effects. DPWG's guideline on DPYD covers tegafur; the findings for S-1 itself come from a few studies.
Every published finding on gene variants and S-1. Upload your DNA file to see which of these rows apply to you.
PharmGKB weighs all studies of a variant and rates how strong the evidence is, from 1A (strongest) to 4.
UGT1A7 UGT1A7*3: Level 3. Toxicity: Colorectal Neoplasms. 1.
UGT1A6 UGT1A6*2a: Level 3. Toxicity: Colorectal Neoplasms. 1.
Studies of how well it worked in people carrying a variant.
Study findings and evidence levels: PharmGKB (CC BY-SA 4.0). Guidelines: CPIC and DPWG, as bundled in PharmCAT. Most studies were done mainly in people of European ancestry.
More drugs from the same category
Not a prescribing recommendation. This page is educational information about pharmacogenomic research and clinical guidelines - it is not medical or dosing advice, and not a prediction of how any medication will work for you. Never start, stop, or change a medication or dose based on it; talk to your doctor or pharmacist, who can order clinical-grade testing if appropriate.
Content updated September 2026.
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