Metformin has been shown as a radiosensitizer in colorectal cancer by causing G2/M phase arrest [26], pancreatic cancer by inhibiting DNA repair to abrogate G2 phase checkpoint [27], esophagus cancer by activating ATM and AMPK [28], HCC by abrogating G2/M phase arrest [29]. The gene discussed is ATM; the disease is hepatocellular carcinoma.