Evaluation of the expression levels of BRAF V600E mRNA in primary tumors of thyroid cancer using an ultrasensitive mutation assay

Abstract

Background: The BRAF V600E gene encodes for the mutant BRAFV600E protein, which triggers downstream oncogenic signaling in thyroid cancer. Since most currently available methods have focused on detecting BRAF V600E mutations in tumor DNA, there is limited information about the level of BRAF V600E mRNA in primary tumors of thyroid cancer, and the diagnostic relevance of these RNA mutations is not known. Methods: Sixty-two patients with thyroid cancer and non-malignant thyroid disease were included in the study. Armed with an ultrasensitive technique for mRNA-based mutation analysis based on a two step RT-qPCR method, we analysed the expression levels of the mutated BRAF V600E mRNA in formalin-fixed paraffin-embedded samples of thyroid tissues. Sanger sequencing for detection of BRAF V600E DNA was performed in parallel for comparison and normalization of BRAF V600E mRNA expression levels. Results: The mRNA-based mutation detection assay enables detection of the BRAF V600E mRNA transcripts in a 10,000-fold excess of wildtype BRAF counterparts. While BRAF V600E mutations could be detected by Sanger sequencing in 13 out of 32 malignant thyroid cancer FFPE tissue samples, the mRNA-based assay detected mutations in additionally 5 cases, improving the detection rate from 40.6 to 56.3%. Furthermore, we observed a surprisingly large, 3-log variability, in the expression level of the BRAF V600E mRNA in FFPE samples of thyroid cancer tissue. Conclusions: The expression levels of BRAF V600E mRNA was characterized in the primary tumors of thyroid cancer using an ultrasensitive mRNA-based mutation assay. Our data inspires further studies on the prognostic and diagnostic relevance of the BRAF V600E mRNA levels as a molecular biomarker for the diagnosis and monitoring of various genetic and malignant diseases.