Molecular signatures in thyroid carcinoma and in its potential precursor lesions

Introduction. The molecular profile of Papillary Thyroid Carcinoma (PTC) has been throughly investigated. However, to date, there is no information regarding the BRAF molecular profile of the non-neoplastic tissue surrounding PTCs. Exploring this molecular signature may help to better understand thyroid tumorigenesis. Aims of this project are: i) to establish whether BRAF mutations are present in non-malignant tissue surrounding PTC and to characterize their activity; ii) to set up a RNA-based panel that may provide diagnostic, predictive and prognostic information on thyroid nodules/neoplasms. Material and Methods. We screened 30 PTCs and 100 non-malignant tissues surrounding the tumor using Next Generation Sequencing. The kinase activity of mutated proteins was evaluated measuring the activation of the MAPK pathway. The RNA-based panel was designed to detect fusion and dysregulated gene-expression, in a set of 44 fresh-frozen samples. Results. Ten (33.3%) PTCs were BRAF-WT and 20 BRAF-positive (66.6%). In 9 non-malignant tissues (9.0%) we identified “uncommon” BRAF mutations. The BRAF-S607F and BRAF-S607P had the same kinase activity of the BRAF-WT protein; the BRAF-A598T and BRAF-G593D proteins showed decreased activity. All “uncommon” BRAF mutations had a lower kinase activity if compared to BRAF-V600E or BRAF-K601E. The samples harboring the BRAF p.V600E mutation or RAS mutations had dysregulated expression of the BRAF-like or RAS-like genes, respectively. Unsupervised hierarchical analysis identified three major clusters: i) non-malignant tissue; ii) malignant tissue; iii) non-follicular thyroid cell derived cancers. Conclusion. Aim 1: non-malignant thyroid tissue may harbor “uncommon” BRAF mutations but without affecting the BRAF-kinase activity and therefore do not possess the tumorigenic potential necessary for the development of PTC. Aim 2: the RNA-based panel identifies three main profiles corresponding to: i) non-malignant tissue; ii) malignant tissue; iii) non-follicular thyroid cell derived cancers. This novel RNA based panel may be very useful to complement the preoperative evaluation of thyroid nodules.