Hereditary breast and ovarian cancer syndrome (HBOC) is clinically defined by family history criteria, and molecularly defined by identification of germline pathogenic variants (PVs) in clinically validated HBOC genes.1 These genes are broadly classified as high-risk genes, increasing breast and or tubo-ovarian cancer risk by at least fourfold, and moderate-risk genes, increasing risk by two- to fourfold  There is a large overlap between clinical and molecular HBOC, i.e. individuals with both family history and a PV. The genetic basis of about half of clinical HBOC, however, is currently unknown or unexplained by singlegene variants,2 and conversely, approximately half of individuals who harbour PVs in HBOC genes do not have a suggestive family history