Cowden disease (CD), or multiple hamartoma and neoplasia syndrome, is a rare autosomal dominant syndrome due to mutation of the PTEN gene. Some patients have a gain-of-function mutation in WWP1, inactivating PTEN. Multiple hamartomatous lesions are associated with a tendency to malignancy of any organ, but particularly of the breast and thyroid.

Typical cutaneous lesions are almost always present and involve the oral mucosa, face, acral areas, palms, and soles. In addition to malignancies of internal organs, benign lesions are frequent, including gastrointestinal (GI) and genitourinary tract polyps and cysts, thyroid adenomas, and hamartomas of the bones, central nervous system (CNS), eyes, and skin.

Most women have severe fibrocystic breast disease, and 20%-36% will develop breast adenocarcinoma. While breast cancer is more likely in females, males have a higher tendency to thyroid cancer. There is also an increased risk of melanoma.

Clinical findings may begin from birth to the fifth decade.