Role of macrophages in tumor development

Macrophages are immune cells that are abundantly present in tumor microenvironment and appear at any stage of tumor development. The microenvironment regulates macrophage activation, and activated macrophages produce cytokines and chemokines that may enhance tumor cell initiation and metastasis, inhibit antitumor immune responses mediated by T cells, and increase tumor angiogenesis and, ultimately, tumor growth. Due to the existence of a complex synergistic relationship between macrophages and tumor cells, tumor-associated macrophages (TAMs) have come to be viewed as possible biomarkers for tumor diagnosis and prognosis, as well as therapeutic targets in these cases. Thus, this chapter focuses on TAMs, its mechanism of tumor progression and metastases, and eventually its application as a therapeutic target for tumors.