Exosomal microRNA: a diagnostic marker for lung cancer.

To date, there is no screening test for lung cancer shown to affect overall mortality. MicroRNAs (miRNAs) are a class of small noncoding RNA genes found to be abnormally expressed in several types of cancer, suggesting a role in the pathogenesis of human cancer. We evaluated the circulating levels of tumor exosomes, exosomal small RNA, and specific exosomal miRNAs in patients with and without lung adenocarcinoma, correlating the levels with the American Joint Committee on Cancer (AJCC) disease stage to validate it as an acceptable marker for diagnosis and prognosis in patients with adenocarcinoma of the lung. To date, 27 patients with lung adenocarcinoma AJCC stages I-IV and 9 controls, all aged 21-80 years, were enrolled in the study. Small RNA was detected in the circulating exosomes. The mean exosome concentration was 2.85 mg/mL (95% CI, 1.94-3.76) for the lung adenocarcinoma group versus 0.77 mg/mL (95% CI, 0.68-0.86) for the control group (P < .001). The mean miRNA concentration was 158.6 ng/mL (95% CI, 145.7-171.5) for the lung adenocarcinoma group versus 68.1 ng/mL (95% CI, 57.2-78.9) for the control group (P < .001). Comparisons between peripheral circulation miRNA-derived exosomes and miRNA-derived tumors indicated that the miRNA signatures were not significantly different. The significant difference in total exosome and miRNA levels between lung cancer patients and controls, and the similarity between the circulating exosomal miRNA and the tumor-derived miRNA patterns, suggest that circulating exosomal miRNA might be useful as a screening test for lung adenocarcinoma. No correlation between the exosomal miRNA levels and the stage of disease can be made at this point.