STK11 (LKB1)(serine/threonine kinase 11) is a tumor suppressor, which regulates the activity of AMPK family members. Simple variants in STK11 are seen in about 1% of all tumors, including 5% of lung tumors and up to 20% of gastrointestinals tumors. Germline variants in STK11 cause the Peutz-Jeghers Syndrome. STK11 variants may predict response to inhibitors of the mTOR pathway.