DNMT1 expression is increased in early stage lung cancer and is implicated in its pathogenesis through the silencing of such genes as RASSF1A and CDKN2A. CDKN2A was not only the first tumor suppressor gene to be found inactivated in lung cancer, but it shows promoter methylation in almost all cancers [24,65,88]. This evidence concerns the gene RASSF1 and lung cancer.