RBP1 and lip and oral cavity carcinoma: Previously, we found a set of retinoid signaling related genes, including ADHFE1, ALDH1A2, CRBP1, PAX9, GDF10, TGFBR3, and PPARγ were frequently hypermethylated and downregulated in OSCC patient samples [7], suggesting the severe molecular defects in RA metabolism in oral cancer.