The increase of the angiogenesis is a prognostic factor in solid tumors. In oncho-hemathology, it is associated to the Myelodysplastic syndromes, Acute Leukaemia and Multiple myeloma. The impact of the raise in the expression of the growing endothelial (VEGF) in the course of chronic myeloid leukaemia (CML) is yet unknown. Yet, there are reports that those patients have presented a higher vascular density in bone marrow (BM) than healthy individuals, specially in blastic phase. Some authors suggest that abnormalities in the angiogenesis may be involved in the phatogenesis in the CML, as well as to its transformation in blastic phase. The increase of the circulating endothelial cells (CEC) is associated to the phatogenesis and to the prognostic of breast cancer and Non-Hodgkin lymphoma, but there are no studies in CML. Thus, we have elaborated a study in order to quantify the CEC in patients with CML in accelerated, chronic and blast phases for flow cytometry. Up to the moment, samples of 46 patients with CML (15 in accelerated phase, 24 in chronic phase and 7 in blastic phase) have been evaluated. Thirty six platelet donors for apheresis with negative sorology were used as a control group. The samples were processed at the same day of the collection, using monoclonal antibodies (MoAb) previously validated in cell of lineage HUV-EC. For the research of the CEC, we used the MoAb CD146 FITC, CD34 PE, CD133 APC e CD62E PE. O AcMo CD45 PC5 was used as a gate strategy for the analysis. The samples were acquired in flow cytometry FACS-Calibur G5 (100.000 events) and analysed in software CellQuest Pro. We noticed an increase statistically significant of CEC in the chronic (p< 0,01), accelerated (p = 0,02) and blastic (p = 0,01) phases of the CML in comparison to the control group, given that these endothelial cells were found in a mature stage. The precursor endothelial cells did not present any statistically significant difference. Patients with LMC present an increment in the amount of CEC in all the phases. The quantification of these cells can be used in the evaluation of therapeutic response, of prognostics and as potential therapeutic target in LMC. The mechanisms involved in the increase of the CEC must be evaluated in future studies. Financial Support: FAPESP

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