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Folate Receptor–Positive Circulating Tumor Cell Detected by LT-PCR–Based Method as a Diagnostic Biomarker for Non–Small-Cell Lung Cancer

Introduction: To investigate the diagnostic performance of folate receptor–positive circulating tumor cells in distinguishing non–small-cell lung cancer (NSCLC) from lung benign disease by using a novel ligand-targeted polymerase chain reaction (PCR) detection technique. Methods: Circulating tumor cells were enriched from 3-ml peripheral blood by immunomagnetic depletion of leukocytes and then labeled with a conjugate of a tumor-specific ligand folic acid and a synthesized oligonucleotide. After washing off free conjugates, the stripped bound conjugates were analyzed by quantitative PCR. Results: Seven hundred fifty-six participants (473 patients with NSCLC, 227 patients with lung benign disease, and 56 healthy donors) were randomly assigned to a training set and a test set. The circulating tumor cell (CTC) levels in patients with NSCLC were significant higher than those with lung benign disease (p < 0.001) and healthy donors (p < 0.001). Compared with carcinoembryonic antigen, neuron-specific enolase, and Cyfra21-1, CTCs displayed the highest area under the receiver operating characteristic curve (training set, 0.815; validation set, 0.813) in the diagnosis of NSCLC, with a markedly sensitivity (training set, 72.46%; validation set, 76.37%) and specificity (training set, 88.65%; validation set, 82.39%). The model combining CTCs with carcinoembryonic antigen, neuron-specific enolase, and Cyfra21-1 was more effective for the diagnosis of NSCLC than tumor makers alone (sensitivity and specificity in the training set, 84.21% and 83.91%; validation set, 88.78% and 87.36%, respectively). In addition, the CTC levels were higher in patients with stage III/IV NSCLC compared with those with stage I/II disease. Conclusion: Ligand-targeted PCR technique was feasible and reliable for detecting folate receptor–positive CTCs in patients with NSCLC, and CTC levels could be used as a useful biomarker for the diagnosis of NSCLC.