CYP26A1 and acute promyelocytic leukemia: CYP26A1 mRNA induction has been reported in skin, intestinal, liver, APL and neuroblastoma cells treated with RA (Armstrong et al, 2005b; Ozpolat et al, 2005; Smith et al, 2006), and CYP26A1 protein is highly expressed in normal human skin (Heise et al, 2006).