BRCA1 and breast cancer: These have largely focused on assessing the risk associated with a polymorphic variation in RAD51. Although there is some evidence that the rare -135G>C variant in RAD51 is involved in modifying the BRCA1/2-mutation-positive breast cancer phenotype, studies focusing on the association between the RAD51 -135G>C and -172G>T variants and breast cancer risk using case-control analysis have shown little support for a significant association with breast cancer [20].