Figure 1.

Schematic diagram of the microenvironment in solid tumors. The tumor microenvironment is a complicated ecosystem of heterogeneous components including tumor cells, stromal cells, and variable types of immune cells, soluble molecules, and extracellular matrix (ECM) components. Stromal cells include endothelial cells, fibroblasts/cancer-associated fibroblasts (CAFs), cancer stem cells, as well as immune cells such as macrophages/tumor-associated macrophages (TAMs), neutrophils/tumor-associated neutrophils (TANs), natural killer cells (NKs), and T cells and B cells. Non-cellular components including ECM exist in a three-dimensional scaffold of extracellular macromolecules, proteins, and polysaccharides that provides structural and biochemical support to cells and soluble molecules (chemokines, cytokines, growth factors, and extracellular vesicles).