A genetic condition characterized by hereditary susceptibility to breast and/or ovarian cancer. It can be defined using family history criteria, or through identification of germline pathogenic variants (GPVs) in clinically validated HBOC genes. However, the genetic basis of about half of clinical HBOC is currently unknown or unexplained by single-gene variants, and approximately half of individuals who harbour PVs in HBOC genes do not have a suggestive family history. [From Orphanet]