BRCA2 and breast cancer: Similar to the embryonic lethality of the RAD51 knockout mouse, initial studies deleting the tumor suppressor gene Brca2 (breast cancer 2, early onset gene) in mice by a targeted deletion that encompasses the eight BRC repeats within exon 11 also resulted in early embryonic lethality, and cells cultured from these embryos exhibited poor proliferation with sensitivity to DNA damaging agents [3,4].