Some genes, like the cell cycle inhibitor p16INK4a (CDKN2A) and estrogen receptor (ER), are frequently hypermethylated across several cancer types, whereas others are more common in specific cancer types, such as hypermethylated DAPK in lung cancer and lymphoma, and GSTP1 in prostate-, breast-, kidney-, and liver cancer [11]. Here, ESR1 is linked to lung cancer.