Fig. 2

The phenotypes of TAMs and their dual roles in tumor progression. Macrophages have dual roles within the TME. Upon their recruitment to the TME, TAMs are believed to polarized into M1-type to restrict tumor progression (left-hand side), or differentiate towards M2-type TAMs to exert a pro-tumor role (right-hand side). M1-like macrophages are known to exert direct phagocytic and cytotoxic effects on tumor cells and induce their apoptosis. Furthermore, serving as the bridge between innate immunity and adaptive immunity, M1 macrophages stimulate the activation of antigen-presenting cells (APCs) and contribute to the immune activation by promoting the recruitment and functions of immunostimulant cells like CD8 + T cells, Th1 cells and NK cells. On the other hand, M2-like TAMs play key roles in cancer initiation and malignant progression by facilitating CSC renewal, stimulating proliferation, supporting tumor-associated angiogenesis, inducing epithelial-mesenchymal transition, favoring tumor cell distant metastasis, enhancing extracellular matrix (ECM) remodeling and suppressing the response to antitumor immunity