Liver kinase B1 (LKB1), also called serine/threonine kinase 11 (STK11), is a ubiquitously expressed serine/threonine kinase originally identified as the tumor-suppressor gene responsible for an inherited cancer disorder, Peutz-Jeghers syndrome (PJS), a rare autosomal dominant intestinal hamartomatous polyposis syndrome associated with perioral melanotic pigmentations and increased risk of cancer, including pancreatic, breast, lung, ovary, and uterine carcinomas [24–26]. Here, MARK2 is linked to Peutz-Jeghers syndrome.