XRCC3 and cancer: Additionally, the commonly studied polymorphisms associated with cancer susceptibility include the substitution of histidine for arginine at codon 188 of exon 3 of the XRCC2 gene (rs3218536) and the transition of C to T at codon 241 of exon 7 of the XRCC3 gene (rs5861539), resulting in the substitution of threonine with methionine [3].