Comparative Transcriptomic Profiling Revealed Distinctive Patterns in Differentially Expressed Genes Related to Clinicopathologic Features of Parathyroid Carcinoma and Adenoma

Parathyroid carcinoma is a rare malignancy which remains as a clinical unmet need lacking effective therapeutic intervention. (1) In this study, we compared mutational profile of parathyroid carcinoma, adenoma, and normal parathyroid tissue using RNA-Seq based transcriptomics analysis and whole exome sequencing. A total of 40 parathyroid specimens [parathyroid carcinoma (n=8), adenoma (n=24), and normal tissue incidentally obtained from thyroidectomy for various reasons (n=8)] from 39 individuals (women n=34, 87%; mean age 51 year) were analyzed. Compared to adenoma and normal parathyroid groups, parathyroid carcinoma group had younger age (carcinoma 35 ± 12 vs. other 56 ± 16 year, p=0.001) and higher serum parathyroid hormone (PTH; 231 [145–474] vs. 114 [88–196] vs. 34 [29–41] pg/mL, p=0.001) prior to surgery. CDC73 mutation was found in 7 of 8 carcinoma specimens, which harbored germline mutation in 6 of them. Among top feature gene mutations for classifying adenoma and carcinoma, carcinoma-specific genes showed high specificity, whereas adenoma-related key features were largely overlapped with normal tissues. Transcriptional profiling revealed 546 carcinoma-specific differentially expressed genes (DEGs), 135 adenoma-specific DEGs, and 323 common DEGs. Hierarchical clustering with 546 carcinoma-specific DEGs detected four clusters with distinctive clinicopathologic characteristics (cluster 1 [n=12]: 7 normal tissues and 5 adenomas; cluster 2 and 3 [n=22]: all adenomas except one normal tissue; cluster 4 [n=9]: all parathyroid carcinomas except one adenoma). Carcinoma-specific DEGs include upregulation of GRIN2A, LYPD1, and SOX2 and downregulation of ENTPPL, MYO3B, and PIK3C2G. Gene ontology enrichment revealed that these DEGs were mainly involved in the binding of cell adhesion molecule, actin, and Rho GTPase, and extracellular matrix structural constituent. Two adenoma clusters significantly differed in urinary calcium excretion level (403 [312–488] vs. 205 [150–327], p=0.037) without significant differences in median PTH (102 [86–138] vs. 125 [92–229] pg/mL) and calcium level (11.1 ± 1.0 vs. 11.0 ± 0.9 mg/dL; P>0.05 for all). In summary, parathyroid carcinoma had distinctive transcriptional profiles which might improve the early detection of parathyroid carcinoma. Parathyroid adenomas were clustered into two groups with regard to urinary calcium excretion level based on transcriptional profiles, which merits further investigation. Reference: (1) Pandya C et al., JCI Insight. 2017 Mar 23; 2(6): e92061. Sources of Research Support: This study was supported by Severance Hospital Research Fund for Clinical Excellence (SHRC C-2019-0032; C-2020-0035).