RAD51 and breast cancer: In fact, we have recently demonstrated that in breast cancer, over 89% of cases lacking competent HR as defined by lack of RAD51 foci formation in an ex-vivo functional assay of HR deficiency harbor a bi-allelic alteration affecting an HR-related gene, and that 89% of breast cancers with bi-allelic inactivation of a HR-related gene are unable to elicit RAD51 foci formation following ex-vivo IR20.