Initiative action of tumor-associated macrophage during tumor metastasis.

Tumor-associated macrophages (TAMs) are a significant component of the microenvironment of any solid tumors in the majority of cancers, associated with unfavorable prognosis. TAMs emerge as attractive targets for therapeutic strategies aimed at reprogramming their protumor phenotype into an effective antitumor activity. In this review article, we present an overview of mechanisms responsible for TAMs recruitment and highlight the roles of TAMs in the regulation of tumor angiogenesis, invasion, metastasis, immunosuppression, and chemotherapeutic resistance. We describe the interplay between Th17 cells and other immune cells in the tumor microenvironment, and we assess both the potential antitumorigenic and pro-tumorigenic activities of Th17 cells and their associated cytokines. Understanding the nature of Th17 cell responses in the tumor microenvironment will be important for the design of more efficacious cancer immunotherapies. Finally, we discuss TAM-targeting therapy as a promising novel strategy for an indirect cancer therapy.