Cowden syndrome (CS), part of a broader category termed PTEN hamartoma tumour syndrome, is characterized by a mutation in the PTEN tumour-suppressor gene, which leads to uncontrolled cell division and the formation of hamartomatous neoplasms and certain cancers, representing an increased lifetime risk of endometrial carcinomas of 13–19 % [54]. The gene discussed is PTEN; the disease is cancer.