Phosphatase and tensin homolog (PTEN) Hamartoma tumor syndrome (PHTS) is a disorder encompassing three seemingly distinct clinical syndromes—Cowden syndrome, Bannayan–Riley–Ruvalcaba syndrome, and Proteus-like syndrome—all of which are characterized by mutations in the tumor suppressor gene PTEN (Phosphatase and tensin homolog)—characterized by unregulated cellular proliferation leading to the formation of hamartomas. The gene discussed is PTEN; the disease is Cowden disease.