XPC and breast cancer: XPC rs2228000 is a C-to-T transition causing a substitution in codon 499 in exon 8 that changes alanine to valine in the interaction domain of XPC with hHRAD23. Consistent with previous reports which linked the TT genotype with lower DNA repair capacity (DRC), [21] this study found that T allele (CT/TT) carriers have a higher breast cancer risk.