Interestingly, various crucial cancer-related genes, such as AHRR, CYP1A1, TNF, SMARCA4, CDK6, RARA, RXRB, CDKN1A, RARG, and NFE2L2, were enriched in the “aryl hydrocarbon receptor signaling pathway” (Supplementary Table S5), through which abnormal epigenetic programming may trigger smoking-attributable cancer (Fig. 1). Here, RARA is linked to cancer.