IL21 and neoplasm: Since the analysis of gene expression pattern in splenocytes of 4T1 tumor bearing young mice treated with calcitriol or its analogs showed increased expression of genes related to Th17 cell lineage such as: interleukin 17a (Il17a), interleukin 17 receptor E (Il17re), interleukin 1 receptor type 1 (Il1r1), Il21, RAR-related orphan receptor alpha (Rora), and RAR-related orphan receptor gamma (Rorc) [33], we focused on the role of Th17 cells population in the activity of calcitriol and its metabolite PRI-2191 in the metastasis process of 4T1 mouse mammary gland cancer in young and aged OVX mice.