OBSERVATIONS Metformin and the Incidence of Cancer in Patients With Diabetes: A Nested

D iabetes is associated with an in-creased risk of various forms ofcancer, such as cancer of the liver, colon, pancreas, breast, bladder, and kid-ney. Metformin, widely given to patients with type 2 diabetes, works by inhibit-ing hepatic glucose production through an LKB1 (serine-threonine liver kinase B1)/AMP-activated protein kinase (AMPK)– mediated mechanism. LKB1 is a well-recognized tumor suppressor. Activation of AMPK by LKB1 plays an important role in inhibiting cell growth. It has been suggested that metformin use in patients with diabetes may reduce their risk of cancer (1). Some studies have reported that diabetic patients taking metformi