Fig. 4.

Colonic M1 and M2 macrophages in the adenoma-carcinoma sequence of sporadic colorectal cancer (CRC). Under physiological conditions, M2 macrophages predominate in the colonic lamina propria. As adenomata develop in the progression to sporadic CRC, M1 macrophages begin to accumulate within the adenoma, possibly in response to the adenoma's compromised epithelial barrier integrity. Following the malignant transformation of the IECs that results in cancer, M2 macrophages become the predominant macrophage in CRC. Cancer cells can harness the anti-inflammatory phenotype of M2 macrophages to prevent immune surveillance and tumoricidal inflammation while exploiting the prohealing and matrix-remodeling activities of M2 macrophages to enhance tumor growth and metastasis.