BRCA1 and breast cancer: Given the likely roles of both BRCA1 and BECN1 in the development of mammary malignancy and the close proximity of BRCA1 and BECN1 genes on chromosome 17q21, large genomic deletions of the 17q21 locus could increase the risk of sporadic breast cancer through loss of expression of both genes, or alternatively, through the loss of only one gene, with loss of the other representing a bystander effect (Laddha et al., 2014).