Studies using DNA methylation as a prognostic biomarker have identified several aggressive tumors with an increased risk of rapid progression and/or relapse (RASSF1 in breast, prostate, squamous cervical cancer; CDH1 in squamous cervical cancer; APC in breast cancer; CDH1 in squamous cervical cancer; CDKN2A in colorectal cancer) [19,21,22]. The gene discussed is CDKN2A; the disease is breast cancer.