BRCA1 and breast cancer: For example, it is well known that carries of mutations in BRCA1/2 are less likely to exhibit human epidermal growth factor receptor 2 (HER2)-postive breast cancers.2 HER2-positive breast cancers are defined by the amplification and/or overexpression of the human epidermal growth factor receptor (HER2/ERBB2) gene at chromosomal region 17q12.