A Prospective Observational Study for Assessment and Outcome Association of Circulating Endothelial Cells in Clear Cell Renal Cell Carcinoma Patients Who Show Initial Benefit from First-line Treatment. The CIRCLES (CIRCuLating Endothelial cellS) Study (SOGUG-CEC-2011-01).

Background: Markers able to predict the response to antiangiogenics in metastatic clear cell renal cell carcinoma (ccRCC) are not available. The development of new treatment options like immunotherapy are reaching the clinic; therefore, predictors of benefit from these different available treatments are increasingly needed.

Objective: In this study, we prospectively assessed the association of circulating endothelial cells (CECs) in peripheral blood with long-term benefit from first-line treatment in ccRCC.

Design, Setting, And Participants: A prospective observational study was designed involving 13 institutions of the Spanish Oncology Genitourinary Group. Adult patients diagnosed with advanced ccRCC who had achieved response or disease stabilization after 3 mo on first-line therapy were eligible.

Outcome Measurements And Statistical Analysis: CECs were isolated from peripheral blood, captured with ferrofluids coated with monoclonal antibodies directed against the CD146 antigen, and assessed centrally with an automated standardized system. CECs were defined as 4',6-diamidino-2-phenylindole+, CD105+, and CD45-. Blood samples were systematically taken every 6 wk for 15 mo or until tumor progression, whichever occurred first. Clinical data were externally monitored at all centers.

Results And Limitations: From August 9, 2011, to January 17, 2013, 75 patients were enrolled in the study. Patients with baseline CECs above the median showed a significantly longer progression-free survival than those with low CECs (22.2 mo vs 12.2 mo) with a hazard ratio of 2.5 (95% confidence interval: 1.2-5.3, p=0.016). There was no difference between CEC levels at baseline and at tumor progression (medians of 50 CECs/4ml and 52 CECs/4ml, respectively).

Conclusions: Under antiangiogenic treatment, the detection of higher CEC levels is associated with clinical benefit in terms of progression-free survival in ccRCC.

Patient Summary: Antiangiogenics are the cornerstone of treatment in kidney cancer. Since they target endothelial rather than tumor cells, we studied the correlation between levels of circulating endothelial cells in peripheral blood and long-term benefit in patients on antiangiogenic therapy. Higher levels were associated with long-term benefit, suggesting that this determination could help to separate best responders from those who could require a more intensive approach.