This includes hypermethylation-mediated silencing of mutL homolog 1 (MLH1), ataxia-telangiectasia mutated (ATM), and O-6-methylguanine-DNA methyltransferase (MGMT), which compromises DNA damage response and contributes to chemo-resistance characteristic of dormant lung cancer cells [36,37,38]. This evidence concerns the gene ATM and lung cancer.