While residing in this PGE2-enriched microenvironment, immature monocytes/macrophages could be inevitably polarized to the M2 phenotype (of course, we did not exclude the activities of other pathways that might mediate the M2 polarization of COX-2+ TAMs; further investigation is needed); besides, the short-range dispersion of PGE2 could also induce M2 differentiation in nearby monocytes/macrophages that had no direct contact with MUC2+ cancer cells (Figure 2, see the COX-2+ TAMs grouped in the stromal region where MUC2 is weakly expressed). Here, PTGS2 is linked to cancer.