Two scenarii might be possible to explain the case: (1) it is sporadic HER2-positive breast cancer developed in a patient with BRCA1 germline mutation and not causally linked to the tumor suppressor gene BRCA1 loss-of-function and in such case we could introduce the notion of incidental genomic event, or (2) it is a rare subgroup of breast cancers occurring in patients carrying BRCA1 germline mutation in which BRCA1 loss of function and HER2 overexpression cooperate in the oncogenesis of the tumor. This evidence concerns the gene ERBB2 and breast cancer.