CXCR4 expression and circulating tumor cell (CTC) counts evaluated as prognostic markers in extensive disease small cell lung cancer (ED-SCLC) patients (pts).

e18558 Background: CXCR4, highly expressed in SCLC, has been implicated in inducing tumor cell migration/invasion and shown to be prognostic of outcome. We evaluated CXCR4 expression in pretreatment CTCs and tumor tissue and post-carboplatin/etoposide (SOC) treatment CTCs in a phase 2 ED-SCLC study of a CXCR4 inhibitor (NCT 01439568). Methods: 89 pts were treated with 42 receiving SOC. CTCs were analyzed using CELLSEARCH CXC kit combined with a PE labelled anti-CXCR4 Ab. CXCR4 expression on CTCs was scored visually by an operator and with specialized software. Baseline tumor CXCR4 expression was quantified (H-score) by immunohistochemistry. Optimum cutoff values for CTC counts and CXCR4 expression on CTCs and tumor were determined from ROC curves. Kaplan Meier curves were used to assess cutoffs as PFS prognostic variables for SOC pts. Results: See Table. For all pts, baseline % CXCR4+CTCs correlated positively with tumor CXCR4 expression (r=0.423; p=0.001). The agreement between operator and software scor...