Both prostate and breast cancer have a heritable component to their aetiology [20]; much of the heritability of prostate cancer is thought to be due to the inheritance of multiple low penetrance susceptibility single nucleotide polymorphisms (SNPs), but inheritance of rarer BRCA1 or BRCA2 gene mutations is known to increase breast cancer risk and to a lesser extent prostate cancer risk. Here, BRCA1 is linked to breast cancer.