THE EXPRESSION OF THE KRAS mRNA ISOFORMS 4A AND 4B IN PLASMA: A COMPARISON BETWEEN LUNG ADENOCARCINOMA PATIENTS AND HEALTHY DONORS THROUGH LIQUID BIOPSY

Background: Liquid biopsy represents an innovative tool in precision oncology to overcome current limitations associated with tissue biopsies. Circulating DNA, but also mRNA could be a useful source of cancer biomarkers. The KRAS gene encodes two splice variants, 4A and 4B. Studies established that the two isoforms are both expressed, the ratio can be altered in tumors, and mutationally activated 4A and 4B both mediate lung carcinogenesis[1]. No data are available about their expression in plasma. We have recently started to collect plasma for a prospective analysis in metastatic lung adenocarcinoma (LA) patients (pts) that are candidate for immunotherapy and chemotherapy. We also started collecting plasma from healthy donors (HD). Herewith we present very preliminary results of a comparison of the KRAS mRNA isoforms (4A and 4B) expression levels between LA pts and HD. Materials and methods: The KRAS isoforms mRNA (4A and 4B) expression levels in plasma were analyzed in 16 LA pts and 5 HD. The plasma from pts was collected at the beginning of the treatment and used to extract the RNA. The RNA was then transcribed in cDNA and 7ng were used to perform the quantitative real-time PCR (RT-qPCR) to detect the KRAS isoforms expression. The RT-qPCR Ct values (the higher value corresponds to a lower mRNA expression level) were converted in Cy0 by a tool for accurate and precise quantification of template and used to compare mRNA expression levels between pts and HD[2]. Data were analyzed with the Mann-Whitney test. Results: The RNA concentration in LA pts and HD was significantly different (p=0.0318): the median concentration value in plasma was 32.3 ng/ml versus 23.5 ng/ml, respectively. A significant difference was also found for the median values of the KRAS isoforms mRNA expression levels between LA pts and HD: Cy0=31.7 versus Cy0=34.6 (p=0.0034), respectively, for KRAS 4A; Cy0=31.5 versus Cy0=34.5 (p=0.0013), respectively, for KRAS 4B. Conclusions: Although in a small size group, these data are very promising. They show a higher concentration of circulating RNA and a higher expression of both the KRAS isoforms in LA pts compared to HD. Patients enrollment is ongoing, and if the data here reported will be still confirmed, circulating KRAS mRNA could be a promising biomarker.