Breast cancer genetics: Syndromes, genes, pathology, counseling, testing, and treatment

Only approximately 10% of breast cancers are caused by identifiable mutations in major breast cancer susceptibility genes. Nevertheless, for families affected by these mutations, genetic testing is a powerful tool for determining which relatives are at high risk and which are not. The list of breast cancer predisposition genes is growing longer with the advent of massive parallel sequencing (next-generation sequencing). BRCA1 and BRCA2 are still the most frequent cause of hereditary breast cancer predisposition with CHEK2, ATM, and PALB2 being the next most common. Most patients with deleterious mutations should consider enhanced surveillance with magnetic resonance imaging, and for some, breast cancer risk will be great enough to consider risk-reducing mastectomy. There are several recently described genes in the Fanconi anemia pathway that are related to BRCA1 and BRCA2. Recognizing mutation carriers at the time of a new breast cancer diagnosis is important for making decisions about surgery, radiation, and systemic therapies.