In the subgroup analysis, the significant odds of the RARβ promoter methylation in tumor tissue was only changed when comparing to sputum (OR = 1.33, 95%CI: 0.98–1.80, P = 0.120) and in subjects with Caucasian ethnicity (OR = 2.38, 95%CI: 0.71–7.92, P = 0.159, Table 2). Here, RARB is linked to neoplasm.