RASSF1 and lung cancer: The lung cancer patient group and the control group were divided into four layers according to the quartile of two genes methylation level, the results showed that the increase of p16 gene and RASSF1A gene correlated with increasing risk of lung cancer(Ptrend<0.05); The median of two genes methylation level was divided into two layers according to the median, the results showed the level of methylation higher than the median will cause increasing risk of lung cancer as seen in Table 3.