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The main treatment for advanced gastric cancer is fluoropyrimidine and platinum-based chemotherapy. We investigated the clinical validitiy of 19 candidate pharmacogenetic variants in ENOSF1 (enolase superfamily member 1), TYMS, CDA, MTHFR, TYMP, DPYD, ERCC1, ERCC2, GSTP1, GSTT1, GSTM1, CYP3A4 and CYP3A5 in relation to overall survival (OS), progression-free survival, objective response rate (ORR) and toxicity in 185 patients receiving triplet chemotherapy. The formal significance threshold was P < 0.0026. TYMS VNTR (variable number of 28-bp tandem repeats) 3 R/3 R genotype was formally associated with inferior ORR (odds ratio (OR) 0.3, P = 0.0025), whereas ENOSF1 rs2612091 G/G was nominally associated with OS after adjustment for TYMS 3 R/3 R (hazard ratio (HR) 1.5, P = 0.041). In a subgroup analysis of patients with locally advanced disease (n = 33), ENOSF1 rs2612091 was strongly associated with OS (HR 6.5, P = 0.001). CYP3A4*22/CYP3A5*3 genotype was nominally associated with grade 3/4 toxicity in patients receiving docetaxel-containing chemotherapy (P = 0.0175). This is the first study suggesting that ENOSF1 rs2612091 is prognostic or predictive of OS in gastric cancer. This finding requires prospective validation.