Methylated CDKN2A (often designated as p16) was an early focus of the search for a plasma diagnostic biomarker for lung cancer; however, while the early studies identified CDKN2A promoter methylation in the plasma of lung cancer patients, they either had very small numbers of healthy controls (Bearzatto et al., 2002), or they did not include a cancer-free control group in their analysis (Kurakawa et al., 2001; An et al., 2002; Ng et al., 2002), extrapolating instead from the lack of CDKN2A methylation in plasma of patients whose tumors were CDKN2A methylation free. The gene discussed is CDKN2A; the disease is lung cancer.