Additionally, 4T1 cells expressed high levels of COX-2 and released PGE2 following in vitro calcitriol treatment.7 Other studies using the 4T1 cancer model have shown that tumor-released PGE2 induces IL-23 production in the tumor microenvironment, causing Th17 cell expansion.57 Both IL-17 and PGE2 may, in turn, stimulate M2 macrophage polarization.58 This evidence concerns the gene IL17A and cancer.