BRCA1 and neoplasm: The BRCA1 gene, situated on chromosome 17q21.31, produces a nuclear protein that plays a role in repairing DNA, regulating the cell cycle, and maintaining the stability of the genome. BRCA1 functions as a tumor suppressor by working with other suppressors, sensors, and transducers to create a complex called the BRCA1-associated genome surveillance complex (BASC).