Purpose: To utilize a novel circulating tumor cell (CTC) technology to quantify ERCC1 expression on CTCs and determine whether ERCC1 expression levels predict efficacy of platinum-based chemotherapy in patients with metastatic non-small-cell lung cancer (NSCLC).
Experimental design: ERCC1 expression was measured in 17 metastatic NSCLC patients who received platinum-based therapy and had ≥2 intact CTCs with acceptable ERCC1 expression assay results. ERCC1 levels were determined from average expression on individual CTCs in each sample. Progression-free survival (PFS) was calculated from the date of therapy initiation.
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 versus 172 days, log-rank, p<0.02) in a Kaplan-Meier analysis using ERCC expression level of 1 as a cutoff (range 0-30). 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). PFS was also observed to decrease with increased cytokeratin (CK) expression (p<0.01 long-rank (Cox regression) and F-test (linear regression)). The hazard ratio is 4.38 (95% CI 1.76-10.9) for each log-change in CK value until progression was noted on imaging.
Conclusion: Low expression of ERCC1 on CTCs correlates with PFS in patients with metastatic NSCLC receiving platinum-based therapy.
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