The tobacco-specific carcinogen, NNK (4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone; also known as nicotine-derived nitrosamine ketone), has been directly linked to the hypermethylation of numerous TSGs in lung cancers whereby exposure to NNK leads to nuclear accumulation of DNA methyltransferase 1 (DNMT1) at gene promoters, resulting in promoter hypermethylation. The gene discussed is DNMT1; the disease is lung cancer.