Table 1.

Cellular components of tumor stroma.

Lineage	Role in tumorigenesis
Tumor-associated macrophages	Immunosuppression; produce cytokines and growth factors Tumor remodeling; secrete matrix metalloproteinases (MMPs) and urokinase-type plasminogen activator (uPA)
Neutrophils	Produce cytokines and reactive oxygen species
Treg cells	Immunosuppression; secrete TGF-β and IL-10 that inhibit the antitumor activity of cytotoxic T-cells and natural killer cells
Th cells	Production of cytokines that induce immunosuppression
B-cells	Production of cytokines and activation of mast cells
Mesenchymal stem cells	Produce cytokines that promote tumor invasiveness and metastasis; Replenish cancer cells
Tumor-associated fibroblasts	Secrete MMPs involved in tumor remodeling; Produce vascular endothelial growth factor (VEGF) that induce angiogenesis
Vascular endothelial cells	Form blood vessels that support tumor growth and metastasis