The BRCA1 and BRCA2 genes are tumor suppressor genes that suppress uncontrolled cell growth. Defects in these genes lead to uncontrolled cell proliferation and an increased risk of cancer in various organs. Located on chromosome 17, the BRCA1 and BRCA2 genes are involved in cell growth, cell division and DNA damage repair. BRCA1 and BRCA2 gene mutations are the most important hereditary mutation risk factors for the development of breast and ovarian cancer. Mutations in these genes cause breast-ovarian cancer syndrome. Approximately 6% of breast cancers and 20% of ovarian cancers are caused by mutations in these genes. In cancer patients with BRCA mutations, the response to chemotherapy is better than in patients without these mutations and therefore treatment success is higher.