Inflammation and Cancer: Extra- and Intracellular Determinants of Tumor-Associated Macrophages as Tumor Promoters

Figure 1

Solid tumors are composed of heterogeneous cell populations, comprising cancer cells, fibroblasts, endothelial cells, pericytes, and leukocytes. Among leukocytes, myeloid cell populations represent a prominent component, in terms of both number and functions, supporting tumor growth and progression. (I) Soluble mediators released by malignant cells or tumor stromal cells recruit different leukocyte populations from the circulation to the tumor site. (II) Infiltrating myeloid cells include immature MDSCs (myeloid-derived suppressor cells) or TAMs. (Factors are listed under (I) and (II) as they appear in the main text.) (III) MDSCs and TAMs exert several protumoral functions such as immunosuppression, angiogenesis, and metastasis. See detailed explanation in the relevant section of the text. CAF: cancer-associated fibroblast; TAM: tumor-associated macrophage; MDSC: myeloid-derived suppressor cell; T-reg: regulatory T-cell.