Immune dysfunction in cancer patients.

Immune deficiency in cancer patients is well documented, and tumor cells have developed a variety of cellular and molecular mechanisms to avoid antitumor immune responses. These mechanisms include defective presentation of tumor antigens on the cell surface and/or an inability of the host to effectively recognize these cells and target them for destruction. Tumor-induced defects are known to occur in all major branches of the immune system. The continuous administration of vascular endothelial growth factor (VEGF), a factor produced by most solid tumors, inhibits the functional maturation of dendritic cells, significantly decreases T-cell to B-cell ratios in the peripheral lymphoid organs, and induces rapid and dramatic thymic atrophy in tumor-bearing animals. VEGF is abundantly expressed by a large percentage of solid tumors, and defective antigen presentation, T-cell defects, and premature thymic atrophy are known to occur in cancer patients and tumor-bearing animals. This review will encompass the major mechanisms responsible for tumor evasion of immune surveillance and highlight a role for VEGF as a principal contributor to tumor-associated immune deficiencies.