Quantification of free RNA in serum and bronchial lavage: a new diagnostic tool in lung cancer detection?

Circulating cell-free nucleic acids have been detected in serum. In cancer patients levels of free DNA seem to be higher than in non-tumor controls and the detectable nucleic acids are partly of tumor origin. We asked whether free RNA can be detected as well in cell-free bronchial lavage fluid (BLF) supernatant, and whether quantification of free RNA allows to discriminate between tumor and non-tumor patients. 73 patients with lung cancer (NSCLC n=62, SCLC n=11) and 56 patients with non-malignant lung diseases were included. The RNA was isolated from 1 mL serum and lavage, respectively with the Quiamp MinElute Virus Vacuum Kit (Qiagen, Germany). A real-time quantitative RT-PCR assay was used for transcript quantification of the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene. Intact RNA was detectable in cell-free supernatants of BLF from 126/129 patients and was investigated in all 64 serum samples. RNA levels were higher in the cell-free supernatant of BLF than in serum. RNA concentration in the BLF from tumor patients was higher than in patients with a benign lung disease (p=0.009). In conclusion, quantification of intact RNA isolated from BLF supernatant and from serum might become a valuable tool for differentiation between tumor and non-tumor patients.