CDKN2A and lung cancer: Aberrant promoter methylation of genes, such as CDKN2A, mutL homolog 1 (MLH1), mutS homolog 2 (MSH2), APC regulator of Wnt signaling pathway (APC), retinoic acid receptor beta (RARB), and O‐6‐methylguanine‐DNA methyltransferase (MGMT) has been described in lung cancer.49