Adjuvant S-1 chemotherapy after curative resection of gastric cancer. Authors' reply

To the Editor—In the February issue of Hong Kong Medical Journal, Yeo et al1 reported an informative study on the use of S-1 as adjunct chemotherapy after curative resection of gastric cancer. Since the active ingredient in S-1 is the prodrug tegafur, to be converted to 5-fluorouracil (5FU), much of the toxicity reduction depends on the degradation of 5FU by dihydropyrimidine dehydrogenase (DPD) encoded by the DPYDgene. For the 0.2% of cases with homozygous defects in DPYD, perhaps Prof Yeo and her colleagues have already provided the answer in their paper when they quoted a Taiwan study in which a single-dose pharmacokinetic study tested the tolerability of S-1 in the individual patient.6 Using a small dose may appear contrary to traditional oncology practice, but in this particular situation it could be a practical and cost-effective way to avoid some alarming outcomes. Clinical relevance of DPYD variants c.1679T>G, c.1236G>A/HapB3, and c.1601G>A as predictors of severe fluoropyrimidine-associated toxicity: a systematic review and meta-analysis of individual patient data.