In addition to Lynch syndrome, rarer genetic conditions-including Cowden syndrome (PTEN), Li-Fraumeni syndrome (TP53), polymerase proofreading-associated polyposis (POLE/POLD1), and hereditary breast and ovarian cancer syndromes (BRCA1/2)-also contribute to hereditary endometrial cancer risk. Here, BRCA1 is linked to Cowden disease.