XRCC1 and breast cancer: A study from the Ontario site of the BCFR, which enrolled both familial and population-based breast cancer cases, observed an interaction between positive family history and the XRCC1 399Q allele.[28] Women in the XRCC1 399R group with a family history were found to have an increase in breast cancer risk, while women in the XRCC1 399Q group with a family history were found to have decreased risk when compared to women without a family history of breast cancer.[28] However, these findings were not statistically significant.