Impact of Endothelial Progenitor Cells on Tumor Angiogenesis and Outcome of Antiangiogenic Therapy: New Perspectives on an Ongoing Controversy
Tumor angiogenesis is driven not only by proliferation of differentiated endothelial cells in sprouting capillaries from pre-existing mature vessels, but also by mobilization of bone marrow derived circulating endothelial progenitor cells (EPCs). The latter are thought to home to the tumor site and incorporate into the lumen of newly growing blood vessels. Over the past several years, a growing number of reports have challenged the hypothesis concerning the involvement of EPCs in tumor angiogenesis, and instead suggest that such cells only have a minor role, if any at all, in the formation of tumor-associated blood vessels. Consequently, these studies implicate EPCs as a minor or negligible target for cancer therapy. In this review, we discuss the arguments for and against a significant role of EPCs in tumor angiogenesis and growth, and as possible surrogate markers of angiogenesis as well as valuable therapeutic targets.
KeywordsTumor Angiogenesis Maximum Tolerate Dose Tumor Blood Vessel Antiangiogenic Drug Mature Endothelial Cell
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