SLC31A1 and digestive system neoplasm: The aim of the study was to evaluate the frequency of alleles and genotypes of DPYD (rs2297595, rs3918290 and rs75017182), ERCC1 (rs3212986 and rs11615), GSTP1 (rs1695), UGT1A1 (rs8175347), CYP3A5 (rs776746), CYP2C8 (rs10509681, rs11572080 and rs1058930), SLC31A1 (rs2233914), CDA (rs2072671), XPC (rs2228001), MTHFR (rs1801133) and TYMS (rs11280056), in a Russian population of patients with gastrointestinal tumors.