Many studies have demonstrated that DNA methylation analysis of specific genes can be used for the early diagnosis of cancer, such as plasma mSEPT9 in colorectal cancer [19], bronchoalveolar lavage fluid SHOX2 and RASSF1A in lung cancer, [20], and urine GSTP1 in prostate cancer [21]. The gene discussed is RASSF1; the disease is lung cancer.