Abbreviations: 5-FU = 5-fluorouracil, CI = confidence intervals, DNA = deoxyribonucleic acid, ECOG = Eastern Cooperative Oncology Group, GC = gastric cancer, HRs = hazard ratios, OS = overall survival, PFS = progression-free survival, PRISMA-P = Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols, RCTs = Randomized controlled trials, RRs = risk ratios, TAS-102 = trifluridine/tipiracil (Lonsurf), TP = thymidine phosphorylase, US = United States. The gene discussed is TYMP; the disease is gastric cancer.