Chemotherapy and the tumor microenvironment: the contribution of circulating endothelial cells

Anti-angiogenic drugs, alone or in combination with chemotherapeutics, are increasingly used by medical oncologists. In many cases, however, their mechanism of action and the tailoring of optimal dosage/schedule are still elusive. Circulating endothelial cell (CEC) and progenitor (CEP) number and viability are modulated in a large series of diseases including cancer, and look promising as surrogate biomarkers for the definition of the optimal biological dose of anti-angiogenic drugs and for patients' stratification. Along with CECs and CEPs, potential EC- and CEP-related surrogate molecular markers such as VE-Cadherin and CD133 are currently under preclinical and clinical investigation.