BRCA1 and cancer: If we consider that BRCA1/2 function as tumor suppressors in normal cells [36], BRCA tumor formation should presumably follow the “two-hit” theory, which would satisfactorily explain the accelerated carcinogenesis that occurs in other familial cancer syndromes [15]; that is, in those individuals with a genetic predisposition to cancer because of an inherited mutated allele in a tumor suppressor gene, it is considered that somatic LOH (i.e., the loss of the healthy allele) is a compulsory step for tumor formation and/or progression in those syndromes.