STK11 and Peutz-Jeghers syndrome: One of the causes of PJS was shown as a loss-of-function mutation in the human LKB1 gene (Hemminki et al. 1998), which is also known as serine–threonine protein kinase 11 (STK11) (Jenne et al. 1998), suggesting that LKB1 protein acts as a tumor suppressor.