title: Increased levels of viable circulating endothelial cells are an indicator of progressive disease in cancer patients.
abstract: BACKGROUND
  There is accumulating evidence from preclinical studies that circulating endothelial cells (CECs) play an important role in neovascularization and tumor growth. The role of CECs in human cancer progression is sparsely investigated. We therefore analyzed CECs in peripheral blood of cancer patients. In addition, we correlated CEC levels in these patients with plasma levels of cytokines that are known to mobilize CECs in experimental models.
  
  
  METHODS
  Viable CECs were isolated, quantified and cultured from cancer patients' whole blood by using magnetic beads coupled to an antibody directed against CD146, a pan-endothelial marker. Viable cells were visualized by calceinAM staining. Positive staining for specific endothelial cell markers [i.e. von Willebrand factor, CD31, vascular endothelial cell growth factor (VEGF) receptor-2] was used to confirm the endothelial phenotype.
  
  
  RESULTS
  Cancer patients with progressive disease (95 patients) had on average 3.6-fold more CECs than healthy subjects (46 patients, P <0.001). Patients (17) with stable disease had CEC numbers equal to that circulating in healthy subjects (P = 0.69). A subset of in vitro cultured CECs incorporated into endothelial layers and formed colonies. Plasma levels of cytokines that are thought to mobilize CECs from the bone marrow [VEGF, placental growth factor, stromal cell derived factor 1alpha and stem cell factor (71 patients)] did not correlate with CEC amounts. The levels of viable CECs in cancer patients were modified by granulocyte colony-stimulating factor treatment and chemotherapy.
  
  
  CONCLUSIONS
  In progressive cancer patients, the amount of CECs is increased. These CECs are viable and may contribute to vessel formation. The number of CECs is influenced by anticancer treatment.
authors.affiliation: Department of Medical Oncology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: L V
authors.initials: LV
authors.lastname: Beerepoot
authors.forename: N
authors.initials: N
authors.lastname: Mehra
authors.forename: J S P
authors.initials: JS
authors.lastname: Vermaat
authors.forename: B A
authors.initials: BA
authors.lastname: Zonnenberg
authors.forename: M F G B
authors.initials: MF
authors.lastname: Gebbink
authors.forename: E E
authors.initials: EE
authors.lastname: Voest
mesh_terms: D020533:Angiogenesis Inhibitors; D014408:Biomarkers, Tumor / Q000032:analysis*; D016207:Cytokines / Q000097:blood; D018450:Disease Progression; D042783:Endothelial Cells / Q000473:pathology; D016228:Endothelial Growth Factors / Q000097:blood; D004730:Endothelium, Vascular / Q000166:cytology* / Q000473:pathology; D005455:Fluorescent Antibody Technique; D005500:Follow-Up Studies; D006801:Humans; D009369:Neoplasms / Q000098:blood supply* / Q000473:pathology*; D009389:Neovascularization, Pathologic / Q000188:drug therapy / Q000473:pathology; D042461:Vascular Endothelial Growth Factor A; D014841:von Willebrand Factor / Q000032:analysis
chemical_list: D020533:Angiogenesis Inhibitors; D014408:Biomarkers, Tumor; D016207:Cytokines; D016228:Endothelial Growth Factors; D042461:Vascular Endothelial Growth Factor A; D014841:von Willebrand Factor