A rare inherited disorder marked by the presence of many benign (not cancer) growths called hamartomas and an increased risk of cancer. Hamartomas form in different parts of the body, especially the skin, mouth, and gastrointestinal tract. Other benign tumors may also occur in the thyroid, breast, uterus, soft tissue, and brain. Other signs and symptoms include a larger-than-average head, abnormal skin changes, blood vessel problems, autism spectrum disorder, and learning and developmental delays. People with Cowden syndrome have an increased risk of developing certain types of cancer, including melanoma and cancers of the breast, thyroid, endometrium, kidney, colon, and rectum. Cowden syndrome is usually caused by mutations (changes) in the PTEN gene. Also called Cowden disease and multiple hamartoma syndrome.