CYP26A1 and leiomyoma: RA regulates a number of genes involved in the RA pathway including the receptors and metabolizing enzymes such as CYP26.12–14 Up-regulation of CYP26A1 expression protects many cell types from apoptosis.15 We have previously demonstrated that CYP26 genes were up-regulated in leiomyomas as compared to myometrial tissue.6 Untreated leiomyoma cells (0 μm) demonstrated a 16·8 ± 4·5-fold up-regulation (P < 0·05) of CYP26A1 gene expression compared with myometrial cells (Table 1).