STK11 and Peutz-Jeghers syndrome: Consistent with these signalling roles, heterozygous mutation of the LKB1 gene in humans leads to the development of Peutz-Jeghers syndrome (PJS), a premalignant disorder characterised by the appearance of pigmentation around the lips, gastrointestinal polyps and an increased risk of all cancers (Boardman et al., 1998).