CRABP2 and head and neck squamous cell carcinoma: Bona fide targets of CRABP2-mediated ATRA signaling such as CRABP2, RARB, and CYP21A1 were demonstrated to be up-regulated due to ATRA treatment in all MPNST cell lines (Table 1) as it was shown in other studies for mouse embryonic carcinoma cells, for COS-7 monkey fibroblast cells as well as for head and neck squamous cell carcinoma cells [64–66].