Circulating endothelial progenitor cells are increased in patients with classic Kaposi’s Sarcoma

Accumulating evidence indicates that tumor angiogenesis is supported by the mobilization and incorporation of endothelial progenitor cells (EPCs), highly proliferative elements derived from the bone marrow. EPCs have been detected at increased frequency in the circulation of patients with different types of cancer. Circulating EPCs have never been quantified in patients with Kaposi’s sarcoma (KS), an angioproliferative malignancy characterized by typical spindle-shaped tumor cells of endothelial origin. In this study, we analyzed the number of EPCs in the peripheral blood of 29 patients with classic KS (cKS) compared with 27 matched healthy controls. EPCs were measured by flow cytometry on fresh blood samples at a single time point. The number of circulating EPCs was significantly higher in cKS patients than controls. EPC count did not correlate with the plasmatic levels of the main proangiogenic factors possibly involved in EPC proliferation and mobilization, thus suggesting that the increased number of EPCs in cKS patients may rather be related to direct or indirect effects of viral environment sustained by HHV-8, the causative agent for KS. The increase of EPCs was significantly more pronounced in cKS patients with slowly evolving than rapidly evolving disease, likely reflecting a localization of EPCs within the lesions during the active phases of KS. Overall, this study demonstrates that EPCs are increased in the peripheral blood of cKS patients and may suggest that changes in the number of circulating EPCs may predict disease progression and may therefore be proposed as a biomarker in the follow-up of KS patients.