The molecular and gene/miRNA expression profiles of radioiodine resistant papillary thyroid cancer

Background Papillary thyroid cancer (PTC) is the most frequent endocrine tumor. Radioiodine (RAI) treatment is highly effective in these tumors, but up to 60% of metastatic cases become RAI-refractory. Scanty data are available on either the molecular pattern of radioiodine refractory papillary thyroid cancers (PTC) or the mechanisms responsible for RAI resistance. Methods We analyzed the molecular profile and gene/miRNA expression in primary PTCs, synchronous and RAI-refractory lymph node metastases (LNMs) in correlation to RAI avidity or refractoriness. We classified patients as RAI+/D+ (RAI uptake/disease persistence), RAI-/D+ (absent RAI uptake/disease persistence), and RAI+/D- (RAI uptake/disease remission), and analyzed the molecular and gene/miRNA profiles, and the expression of thyroid differentiation (TD) related genes. Results A different molecular profile according to the RAI class was observed: BRAF.sup.V600E cases were more frequent in RAI-/D+ (P = 0.032), and fusion genes in RAI+/D+ cases. RAI+/D- patients were less frequently pTERT mutations positive, and more frequently wild type for the tested mutations/fusions. Expression profiles clearly distinguished PTC from normal thyroid. On the other hand, in refractory cases (RAI+/D+ and RAI-/D+) no distinctive PTC expression patterns were associated with either tissue type, or RAI uptake, but with the driving lesion and BRAF-/RAS-like subtype. Primary tumors and RAI-refractory LNMs with BRAF.sup.V600E mutation display transcriptome similarity suggesting that RAI minimally affects the expression profiles of RAI-refractory metastases. Molecular profiles associated with the expression of TPO, SLC26A4 and TD genes, that were found more downregulated in BRAF.sup.V600E than in gene fusions tumors. Conclusions The present data indicate a different molecular profile in RAI-avid and RAI-refractory metastatic PTCs. Moreover, BRAF.sup.V600E tumors displayed reduced differentiation and intrinsic RAI refractoriness, while PTCs with fusion oncogenes are RAI-avid but persistent, suggesting different oncogene-driven mechanisms leading to RAI refractoriness. Keywords: Thyroid, Oncogenes, Radioiodine refractory, Gene/miRNA profiles, Papillary thyroid cancer