RARB and non-small cell lung carcinoma: Increasing evidence suggests that gene methylation may become a potential diagnostic biomarker in NSCLC (i.e., P16, RASSF1A, APC, RARβ, DAPK and CDH13) [37, 38], and serve as a prognostic biomarker such as P16 and RASSF1A [39, 40].