Abstract
Platelets (PLTs) contain an assortment of growth factors (GFs), in particular PLT-derived GFs (PDGFs), transforming GFs (TGFs), and vascular endothelial GF (VEGF) (1). By topical release and action of these GFs simultaneously with thrombus formation and bleeding cessation, PLTs initiate the processes of wound repair, angiogenesis, and defense against infectious agents (1). Released GFs may also have distant effects if they reach the fluid compartment of the circulating blood. Increased serum PDGF concentrations during and after hemodialysis, attributable to PLT-membrane contact at artificial surfaces, may be directly involved in the increased frequency of atherosclerosis in hemodialysis patients (2). The role of circulating GFs in many other nonmalignant clinical conditions has also been investigated (3)(4)(5)(6)(7)(8). Increased concentrations of VEGF have been found in a wide spectrum of malignancies (9)(10)(11)(12)(13)(14)(15)(16). Many researchers assume a prognostic relevance of this finding because VEGF is crucial in angiogenesis, which in turn is crucial for metastasis and tumor growth (9)(11). The question of whether serum or plasma is the best specimen to use for the measurement of circulating VEGF has not been answered. Increased VEGF concentrations in cancer are detectable in serum and plasma. The concentrations are much higher in serum than in plasma, however, because VEGF is released from PLTs in vitro during the clotting process (9)(11)(12). Nevertheless, many researchers prefer to measure serum VEGF because combined cellular and soluble GFs act at the tumor site (12)(13)(15). Furthermore, PLTs may act as scavengers for tumor-derived GFs (10)(15)(16). Although EDTA …
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