Correlation Of Ercc1 Expression On Circulating Tumor Cells With Progression-Free Survival In Metastatic Non-Small Cell Lung Cancer Patients Treated With Platinum-Based Chemotherapy

10574 Background: Biomarkers predicting efficacy of chemotherapy are highly desirable. Fiber array scanning technology (FAST) is a novel method of detecting circulating tumor cells (CTCs) that does not employ an EpCam enrichment step. The purpose of this study was to use FAST to evaluate ERCC1 expression on CTCs to determine whether ERCC1 expression correlates with progression-free survival (PFS) in patients who received platinum-based chemotherapy for metastatic non-small-cell lung cancer (NSCLC). Methods: Peripheral blood from one hundred enrolled patients with metastatic NSCLC was collected by two institutions (Stanford Cancer Institute and Billings Clinic Cancer Center). FAST was used to identify individual CTCs on immunofluorescence by pancytokeratin antibodies. Nuclear localization of ERCC1 expression by immunofluorescence was quantified on individual CTCs. Total patient ERCC1 levels were determined from the average expression of all the CTCs in each patient sample. Fifty-seven of the one hundred patients enrolled received platinum chemotherapy. Seventeen of those fifty-seven patients (30%) had ≥ 2 evaluable intact CTCs and were analyzed retrospectively. Linear regression (F-test) was used to evaluate the correlation between ERCC1 expression and PFS. Kaplan-Meier survival analysis (log-rank test) was used to compare PFS in patients with CTCs with no detectable ERCC1 expression versus patients with CTCs that expressed any level of ERCC1. Results: PFS decreased with increasing ERCC1 expression (P<0.04 F-test, linear regression). Lack of ERCC1 expression was associated with longer PFS (266 days vs. 172 days, log-rank test P<0.02). The difference in survival was statistically significant with a hazard ratio of 4.20 (95% CI 1.25-14.1, p<0.02, log-rank test). Conclusions: In this small study, using FAST to isolate CTCs, low expression of ERCC1 on evaluable CTCs correlated with increased PFS in patients with metastatic NSCLC who received platinum chemotherapy. A larger, prospective study to validate these retrospective results is warranted.