Circulating endothelial cells as a novel marker of angiogenesis

Measurement of tumor angiogenesis to predict and/or to assess the efficacy of antiangiogenic therapies is mainly based on the evaluation of microvessel density (MVD). We developed a novel flow cytometry procedure to measure circulating endothelial cells (CECs) and circulating endothelial cells progenitors (CECPs) in either preclinical and clinical studies. Preclinical studies were performed on an animal model of human lymphoma. A trend toward higher CECs values was observed on day 7 and 14 after transplant, and differences vs controls were highly significant on day 21 (p=0.0061). A strong correlation was found between CECs and tumor volume (r=0.942, p=0.004) and between CECs and tumor-generated VEGF (r=0.669, p=0.02). In mice given cyclophosphamide, most of circulating apoptotic cells were hematopoietic and not endothelial. Conversely, in mice given endostatin, all of the increase in apoptotic cells was in the endothelial cell compartment. In a parallel study, we looked for CECs in the peripheral blood of 20 healthy controls and 76 newly diagnosed cancer patients by means of four-color flow cytometry. In breast cancer (n=46) and lymphoma (n=30) patients, both resting and activated CECs were increased by 5 fold (P