Abnormal expression of let-7a microRNA (miRNA) in non-small cell lung cancer (NSCLC) cells and tissue has been previously reported. Our objective was to investigate whether let-7a miRNA is aberrantly expressed in the blood of NSCLC patients. Using real-time PCR (RT-PCR), we analyzed let-7a miRNA in archived whole blood from 65 participants, 35 of whom had NSCLC and 30 of whom did not. Using RT-PCR, we also investigated the expression of let-7a miRNA in NSCLC cell lines (A549 and HCC 1588), a normal human lung fibroblast cell line (WI-38) and in 40 human NSCLC tissues. The 2-ddCt of let-7a miRNA in the blood of normal subjects and those with NSCLC was 3242.49±355.28 and 747.85±177.74, respectively. The relative expression of let-7a miRNA in the A549 and HCC 1588 cancer cell lines was approximately 0.3 and 0.35, respectively, compared to WI-38 cells. The 2-ddCt of let-7a miRNA in the normal human lung tissues and human NSCLC tissues was 42.30±3.98 and 27.73±3.86, respectively. Let-7a miRNAs were under-expressed in the blood of NSCLC patients, as well as NSCLC cells and NSCLC tissues, compared to normal controls. The possibility of using let-7a miRNA as a serologic marker for lung cancer warrants further study.

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