Studies of Benign and Malignant Thyroid Disease

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Background: Thyroid microcarcinomas (TMCs) are tumors measuring 1cm characterized by an indolent behavior. However, up to 10% of TMCs may present with clinically significant lymph node (LNM) or distant metastases (DM). The characterization of molecular signature of metastases-prone TMCs may help strategizing the management options. Methods: We performed whole transcriptome sequencing on the RNA extracted from 95 tissue samples, using KAPA RNA HyperPrep Kit. Eleven samples failed quality check. Differential expression analysis was performed using the LCDB workflow, with adjusted p-value0.1 rendered significant. Results: The study cohort consisted of 19 patients with lateral neck LNM and/or DM (N1b group) and 17 patients without metastases (N0/Nx). There was no difference in the histology breakdown (p=0.5), median primary tumor size (0.6cm vs 0.8cm, p=0.27), age (39y vs 46y, p=0.54), gender (p=0.32) between the study groups. There were 93 differentially expressed genes (DEGs) in the primary tumors of pN1b patients versus pN0/pNx (8-up and 85-down-regulated; padj0.1). Primary tumors from N1b group were characterized by a significant downregulation in antigen binding immune components (CD19, CD79A, CR2; log2FC>-2.6; padj<0.05), immunoglobulin receptor binding/structure (IGHV1,3,4-family, FCRLA; log2FC>-2.6; padj<0.05) or in the development and differentiation of B-cells (PAX5, MS4A1; log2FC>-2.7; padj<0.05), and a significant upregulation of integral components of the membrane (NUP210L, TMEM145; log2FC>2 and padj<0.05) and extracellular protease (ADAMTS4; log2FC>2; padj<0.05). The paired analysis of LNM vs primary tumor revealed 518 DEGs (322-up and 196-down; padj 0.1). LNM were characterized by a significant downregulation of the genes coding for tight junction proteins (CLDN6, CLDN4; log2FC>-0.9; padj<0.001), components of voltage-gated potassium channels (KCNJ12, KCNA1; log2FC>-0.8; padj<0.05), and G-protein coupled receptor signaling (ARHGEF35, GPRC5A; log2FC>-0.5; padj<0.05), while the up-regulated genes included members of non-receptor tyrosine kinase families (BLK, TXK; log2FC>1.7; padj<0.01), immune components (MS4A1, CR2, FCRL2, FCMR; log2FC>1.9; padj<0.01) and integral membrane components (TMEM272, PCDH15, SHISAL2A; log2FC>1.7; padj<0.01). Conclusions: TMCs associated with LNM and/or DM are characterized by dysregulated immune landscape compared with classic indolent TMCs, suggesting a decreased immune response as a factor predisposing to metastases. Metastatic lesions are characterized by decreased tight junctions that are involved in signal transduction as one of the hallmarks of progression.