Comparison of TERT and 5-hydroxymethylcytocine immunohistochemistry in various thyroid carcinomas

Telomerase reverse transcriptase (TERT) promoter mutation is associated with an aggressive clinical course in thyroid carcinomas. Therefore, detection of TERT promoter mutation is essential for proper patient management. 5-Hydroxymethylcytosine (5hmC) is an epigenetic marker involved in the DNA demethylation pathway, and its loss has been observed in various tumors. Loss of 5hmC has also been reported in thyroid carcinomas and is presented as a possible predictive biomarker for TERT promoter mutation and worse prognosis. This study evaluated the expression of TERT and 5hmC by immunohistochemistry (IHC) in 105 patients (44 in the TERT mutant group and 61 in the TERT wild group) with various thyroid carcinomas. H-scores were calculated using an image analyzer. The median H-scores of TERT IHC were significantly higher in the TERT mutant group than in the TERT wild group (47.15 vs. 9.80). The sensitivity and specificity of TERT IHC for predicting TERT promoter mutations were 65.9 and 65.7 %, respectively. Regardless of TERT promoter mutation status, the 5hmC H-scores were markedly lower in all subtypes of thyroid carcinomas compared to those in their normal counterparts. Significant differences in 5hmC H-scores were observed between N0 and N1 in total thyroid carcinomas, but not within the papillary thyroid carcinoma subgroup. In conclusion, TERT and 5hmC IHC have limitations in predicting the presence of TERT promoter mutations. The expression of 5hmC was downregulated in various thyroid carcinomas compared to that in normal and benign lesions, but comprehensive further studies are required to elucidate the role of 5hmC in thyroid carcinomas.