Figure 1.

Sources of tumor microenvironment (TME). The TME has been divided into seven specialized microenvironments to investigate the tumor–stroma interactions: metabolic microenvironment, immune microenvironment, hypoxic microenvironment, acidic microenvironment, innervated niche, mechanical microenvironment, and microbial microenvironment (containing gut and intra-tumor microbiota). These specialized microenvironments engage in crosstalk to work together on the tumor and the entire organism. Adapted from reference [2]. MDSC, myeloid-derived suppressor cell; CAF, cancer-associated fibroblast; TAM, tumor-associated macrophage; DC, dendritic cell; ECM, extracellular matrix; PNI, perineural invasion.