USP39 and cancer: Genes with recurrent never-smoker-specific hypoDMRs in the promoter include ASPSCR1, a known fusion oncogene whose methylation is linked to prenatal smoking and reduced lung function [30]; the DNA topoisomerase TOP2A, a pan-cancer up-regulated gene [31], [32]; and DPP9 and USP39, which have been implicated in lung cancer [33], [34].