PTEN and hamartoma: 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.