STK11 and Peutz-Jeghers syndrome: Encodes serine/threonine kinase 11 that regulates cell polarity and acts as a tumor suppressor. Mutations in STK11 are associated with Peutz-Jeghers syndrome, which is characterized by the growth of polyps in the gastrointestinal tract, pigmented macules on the skin and mouth, and other neoplasms.