Tumor-Associated Myeloid Cells in Cancer Progression

Abstract

The tumor microenvironment plays a pivotal role in orchestrating tumor initiation, progression, and spreading, as well as response to therapy. Myeloid immune cells infiltrating tumors are integral component of the TME. While it would be expected that immune cells exert mainly a protective role for the host against tumor, it is now well established that tumor cells can strongly influence the functions of immune cells, subverting their biological properties and enabling them to support the neoplastic growth. Tumor-associated macrophages (TAMs) and neutrophils (TANs), together with myeloid derived suppressor cells (MDSCs) are the most representative myeloid cells infiltrating tumors. They are a very heterogeneous entity of cells regulating diverse aspects of cancer biology, directly supporting cancer growth and survival, angiogenesis, metastasis as well as immunosuppression. Given these premises, innovative anti-cancer approaches consider targeting of myeloid cells an essential aspect for the success of the therapy. Here, we will review the main characteristics of tumor-associated myeloid cells and their role in promoting tumor growth and dissemination. In addition, we will briefly address the therapeutic possibilities based on targeting of these cells.