BRCA1 is a multifunctional protein involved in maintaining genomic stability via DNA repair and recombination, tumor suppression, and cell replication. Dysfunction of BRCA1 through inherited or somatic mutation or via epigenetic silencing is the oncogenic source of a certain percentage of breast cancers. Mutations in this gene are responsible for up to 80% of inherited breast and ovarian cancers, and can also predispose individuals for other malignancies such as pancreatic cancer. Immunohistochemistry (IHC) staining and testing for wild type and mutated forms of this repair gene are thus necessary for diagnosis and downstream treatment. In IHC of normal tissue, BRCA1 has nuclear and cytoplasmic positivity in populations of cells in most tissues throughout the body. References: Anticancer Agents Med Chem. 2015;15(1):4-14, PMID: 25329591; “BRCA Mutations: Cancer Risk and Genetic Testing.” National Cancer Institute, URL: https://www.cancer.gov/about-cancer/causes-prevention/genetics/brca-fact-sheet; Nature. 2017 Oct 19;550(7676):360-365, PMID: 28976962