Since calcitriol increases the expression of CYP2R1 and VDR in endometrial explant tissues (this study) and in human endometrial cancer [24] and oral squamous carcinoma cells [46], it is likely that calcitriol at the maternal-conceptus interface may affect the expression of CYP2R1 and VDR in chorioallantoic tissues. This evidence concerns the gene CYP2R1 and endometrial cancer.