Metformin, an oral biguanide anti-hyperglycemic agent, reportedly enhances responses to radiation by activating ataxia telangiectasia mutated (ATM)-adenosine monophosphate kinase (AMPK)-p53/p21cip1, which leads to apoptosis and inhibition of clonogenic survival [15, 16] in certain cancers. The gene discussed is ATM; the disease is cancer.