Circulating endothelial cells as biomarkers in clinical oncology.

Circulating endothelial cells (CECs) and circulating endothelial progenitors (CEPs) play a different role in cancer development, acting as possible markers of vascular turnover/damage (CECs) and vasculogenesis (CEPs). Preclinical and clinical data suggest that CEC enumeration might be useful to define the best treatment option for patients who are candidate to anti-angiogenic therapy, while CEPs seem to have a "catalytic" role in different steps of cancer progression and recurrence after therapy. The definition of CEC and CEP phenotype and the standardization of CEC and CEP enumeration procedures are highly warranted to use these cells as biomarkers in clinical trials in oncology, and to compare results from different studies.