When NSCLC was compared to SCLC (Figure 6), our results demonstrated that the methylation of the P16, RASSF1A, APC and SHOX2 genes was significantly correlated with tumor histology, and the methylation levels of the SHOX2 and RASSF1A were significantly lower in NSCLC than in SCLC (OR = 0.19, 95% CI = 0.07 - 0.49, P = 0.001; and OR = 0.06, 95% CI = 0.03 - 0.13, P < 0.001, respectively). This evidence concerns the gene APC and non-small cell lung carcinoma.