Furthermore, receptor activator of nuclear factor-κB (RANK) and its ligand (RANK-L) play an essential role in breast development during pregnancy72,73 and RANK and RANK-L have been shown to promote BC in mice with a Brca1 variant.74 These preclinical studies are consistent with the idea that BRCA1 may have unique functions during a reproductive cycle. The gene discussed is BRCA1; the disease is breast cancer.