Peutz–Jeghers syndrome (PJS) is an autosomal dominant disease caused by mutations of the serine-threonine kinase 11 (STK11/LKB1) gene, a tumor suppressor gene that determines hamartomatous gastrointestinal polyposis and typical mucocutaneous pigmentation [62,63]. Here, STK11 is linked to Peutz-Jeghers syndrome.