PTEN hamartoma tumor syndrome refers to a spectrum of conditions that are characterized by multiple hamartomas. These conditions include: Cowden syndrome - associated with a high risk for benign and malignant (cancerous) tumors of the thyroid, breast, and uterus. Affected people may also have macrocephaly and characteristic skin abnormalities. Bannayan-Riley-Ruvalcaba syndrome - characterized by macrocephaly (large head size), hamartomas of the intestines (called hamartomatous intestinal polyps), and dark freckles on the penis. Proteus syndrome - characterized by overgrowth of the bones, skin, and other tissues. Proteus-like syndrome - people with many of the signs and symptoms associated with Proteus syndrome, but who do not meet the diagnostic criteria. PTEN hamartoma tumor syndrome is caused by changes in the PTEN gene and is inherited in an autosomal dominant manner.