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CD276-positive circulating endothelial cells in advanced colorectal cancer.

572 Background: The value of circulating endothelial cells (CECs) as predictive biomarker in metastatic colorectal cancer (mCRC) may be improved by using tumor-derived CECs. CD276 can discriminate between tumor derived and normal CECs. We evaluated whether CD276+CEC is a clinically relevant biomarker with 100% sensitivity to predict response to first line palliative combination systemic therapy with fluoropyrimidine and oxaliplatin in patients with mCRC. Methods: Samples were prospectively collected from patients with mCRC enrolled in the ORCHESTRA trial. At baseline and at first evaluation (after 4 cycles of 5-FU/LV or 3 cycles capecitabine with oxaliplatin ± bevacizumab), CECs were measured by flowcytometry with a previously validated panel (CD34+CD45-CD146+DNA+; and additional CD276+ for tumor derived CECs). A clinically relevant cut-off value of (CD276+) CECs was determined as 100% sensitivity (and 80% specificity in 95% CI) identifying patients with progressive disease within 6 months. Results: There were 182 baseline samples, from which 133 follow up samples were available for analysis. CEC and CD276+CEC counts significantly increased during treatment from 48 to 90 CEC/4 ml (p = 0.00) and from 14 to 33 CD276+CEC/4 ml (p = 0.00) at baseline and at first evaluation, respectively. In patients treated with bevacizumab, CEC counts were lower after three cycles compared to patients treated with chemotherapy alone 75.5 vs 131 CEC/4ml (p = 0.04), 28 vs 41 CD276+CEC/4 ml (p = 0.08). Baseline values nor changes in CEC and CD276+CEC counts were predictive for poor response (progressive disease within 6 months, AUC 0.53 for CEC and AUC 0.52 for CD276+CEC). Conclusions: Despite numerical changes during therapy, CEC and CD276+CEC counts do not adequately predict poor response to first line palliative systemic therapy in patients with mCRC. (NCT01792934.)