In our study, the 399-Gln allele of XRCC1 increased significantly the risk of BC and it may act as a dominant allele [Arg/Arg vs. (Gln/Gln + Arg/Gln), OR = 4.67 (95% CI 1.65-13.23), p = 0.005]. The combination of variant alleles at codon 399 and in position -77 could affect XRCC1 protein activity, impairing genome integrity and promoting cancer occurrence. Also, the number of SNPs in several genes involved in BER and HRR mechanisms made higher the risk of sporadic BC. We can conclude that genetic variants in multiple repair pathways may have a joint or additive effect in cancer risk.

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