1. Role of circulating endothelial cells in the evaluation of response to chemotherapy in non-small cell lung cancer patients M. Salamoon(1), M al AMMAR¹ (1)Bairouni University Hospital, Damascus, Syria Background: The majority of NSCLC cases diagnosed in advanced stages, which make the treatment non-curative with high recurrence rate. So it is very important to define a biological marker to aid us as a predictive factor. When the tumour volume become at 1–2mm, it begin the stimulation of endothelial cells by a multiple growth factors to generate a new vessels, so the circulating endothelial cells (CECs) increase in the blood stream theoretically. Many methods used to discover these cells as Immunomagnetic Separation (IMS) technique, four-color channels flow cytometry and PCR. The phenotype of these cells can be defined by the positivity of CD146 and CD31 while the CD45 is negative. Increased number of CECs was found in tumours. Many studies confirmed the normalisation of CECs levels in cancer patients after the treatment. Mancuso et al. confirmed the importance of quantify these cells to evaluate the response of chemotherapy in breast cancer. Materials and Methods: Newly diagnosed patients with non surgical stages III or IV NSCLC have been included. Blood samples have been taken before starting any treatment then after 3 cycles of chemotherapy to evaluate the number of CECs by using IMS techniques with a Nageotte slide by a fluorescent microscope equipped with camera. Results:143 naive patients of have recruited. Before treatment the number of CECs was more than 80 cells/ml in 121 patients [45 pts. (81–150 c/ml), 32 pts. (151–300 c/ml) and 43 pts. More than 300 cells/ml] while, just 22 patients with less than 80 cells/ml. (79) patients were valuable after 3 cycles. The difference between CECs accounts before and after treatment was calculated as relative absolute quotient (ΔaCECs) has been considered significant when it was more than 0.1. Accordance between CECs and response to treatment was found in 61 patients (77%). The account of CECs was significantly decreased in 42 patients who showed Partial Response, while 11 patients with progression disease had significant increased number of CECs and 8 patients with Stable disease with no significant changes in CECs number. On the other hand, 18 patients (23%) didn't show accordance between the treatment response and CECs levels. Conclusions:CECs seem to be a predictive factor in evaluating response to chemotherapy in NSCLC patients. However, further studies are necessary to evaluate the role of CECs levels in the recurrence prediction.