Following a large literature review (Wrangle et al. 2014; Yin et al. 2012; Yang et al. 2019; Li et al. 2020; Chen et al. 2020; Hulbert et al. 2017; Brait et al. 2012; Di Vinci et al. 2012; Hwang et al. 2015; Ooki et al. 2017; Zeng et al. 2019; Zhao et al. 2016; Song et al. 2015), we explored the performance of the DNA methylation of 7 genes including TAC1, CDO1, HOXA9, ZFP42, SOX17, RASSF1A and SHOX2 in the blood cfDNA samples in distinguishing lung cancer from benign nodules and healthy individuals. The gene discussed is HOXA9; the disease is lung cancer.