Vascular endothelial growth factor measured in platelet poor plasma allowsoptimal separation between cancer patients and volunteers: A key to study an angiogenic marker in vivo?

Background: Serum VEGF levels are elevated in cancer patients and are used as a tumor marker in different malignancies. We have measured VEGF levels i n different blood compartments in cancer patients and healthy volunteers in order to assess the most suitable way of processing blood for measuring VE GF as a marker of tumor-angiogenesis. Patients and methods: VEGF concentrations were analyzed by an enzyme-linked immunosorbent assay in serum (VEGF(S)), EDTA plasma (VEGF(E)DTA), citrated plasma (VEGF(C)), CTAD-plasma (VEGF(C)TAD), platelet poor plasma (VEGF(P)P P), platelet rich plasma after induction of platelet activation (VEGF(P)RP) . Platelet activation was assessed by measuring PF4 concentrations in diffe rent plasma samples. Results: We observed higher VEGF(S) (P = 0.0027), VEGF(E)DTA (P = 0.003) an d VEGF(P)PP (P = 0.0007) levels in cancer patients than in volunteers; VEGF (P)RP concentrations showed no significant difference (P = 0.208). Analysis of the correlation between VEGF(p)lt and VEGF(S) in cancer patients showed a similar correlation in a comparable VEGF(S) concentration range as in th e volunteers. When comparing VEGF(C) to VEGF(C)TAD, we find significantly h igher VEGF and PF4 levels in citrated plasma (VEGF: P = 0.00019; PF4: P = 0 .00023). Conclusions: It is likely that VEGF(S) in cancer patients encompass platele t-delivered VEGF and VEGF from other sources, notably from (neo)-angiogenes is in tumoral tissue. The best discrimination between volunteers and cancer patients was observed in PPP. As generating plasma can induce platelet act ivation, with consequent VEGF release from platelets, we suggest that to as sess free circulating VEGF, CTAD plasma should be used.