RARB and neoplasm: Prominent nuclear staining of the intracellular transporters CRABP2 and FABP5, as well as nuclear receptors RARα, RARβ and PPARβ/δ were detected in basal and supra-basal keratinocytes of normal mucosa, while a more heterogeneous expression pattern concerning staining intensity and intracellular localization of all five proteins was found in tumor cells (Fig. 1a).