The inflammatory micro-environment in tumor progression: The role of tumor-associated macrophages

The link between inflammation and cancer proposed more than a century ago by Rudolf Virchow, who noticed the infiltration of leukocytes in malignant tissues, has recently found a number of genetic and molecular confirmations. Experimental, clinical and epidemiological studies have revealed that chronic inflammation contributes to cancer progression and even predisposes to different types of cancer. Cancer-associated inflammation includes: the presence of leukocyte infiltration; the expression of cytokines such as tumor necrosis factor (TNF) or interleukin (IL)-1; chemokines such as CCL2 and CXCL8; active tissue remodelling and neo-angiogenesis. Tumor-associated macrophages (TAM) are key regulators of the link between inflammation and cancer. Many observations indicate that, in the tumor micro-environment, TAM have several protumoral functions, including expression of growth factors, matrix proteases, promotion of angiogenesis and suppression of adaptive immunity. In this review we will discuss the role of TAM in the inflammatory micro-environment of solid tumors and will try to identify potential target for future therapeutic approaches.