CYP26B1 and cancer: ISH on tissue sections obtained from mT5 tumors after administration of Am80 showed that the expression of Cyp26b1, the gene encoding an RA-metabolizing enzyme, the expression of which is activated by RA [35], was mainly upregulated in spindle-shaped stromal cells, but not in mT5 tumor cells in response to Am80 administration, supporting the notion that Am80 does not directly target tumor cells in these murine cancer models (Supplementary Fig. S10C).