The role of tumor-associated macrophage in tumor progression

The tumor progression is not only regulated by metastasis promoting and suppressing genes in cancer cells but it is also strongly influenced by the interaction between cancer cells and the stromal cells. An abundance of inflammatory mediators and leukocytes has been known to promote cancer metastasis, and tumor associated macrophages (TAM) are the key players in the link between inflammation and cancer. TAM are derived from peripheral blood monocytes that are recruited into the tumor by inflammatory chemokines. Upon activation by cancer cells, TAM gain the ability of pro-tumoral functions including expression of various growth factors, promotion of angiogenesis and suppression of adaptive immunity, and many of these factors also play critical roles in cancer metastasis. In this review, we will summarize the recent information about the function of TAM in the inflammatory micro-environment of solid tumors and discuss the potential targets for future therapeutic approaches.