CYP26A1 and leukemia: Various investigators have found a dose-dependent up-regulation of CYP26A1 by ATRA in different cell types.12,13 In leukaemia cells, ATRA can induce CYP26A1 at doses of 1 μm,12 whereas in endothelial cells, 10 μm ATRA was required to induce expression of CYP26A1.13 Our results demonstrated that CYP26A1 transcripts were up-regulated in myometrial cells exposed to ATRA when compared to unexposed cells.