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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 54  |  Issue : 5  |  Page : 171-176

Significance of telomerase reverse-transcriptase promoter mutations in differentiated thyroid cancer


Department of Surgery, MacKay Memorial Hospital and Mackay Medical College, Taipei, Taiwan

Date of Submission30-Nov-2020
Date of Decision11-Jan-2021
Date of Acceptance30-Jun-2021
Date of Web Publication12-Oct-2021

Correspondence Address:
Shih-Ping Cheng
No. 92, Chung-Shan North Road, Section 2, Taipei 104215
Taiwan
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/fjs.fjs_212_20

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  Abstract 


Background: Telomerase reverse-transcriptase (TERT) encodes the reverse transcriptase of telomerase, and TERT promoter mutations are enriched in advanced thyroid cancer. In this study, we aimed to characterize the clinicopathologic biology of differentiated thyroid cancer harboring TERT promoter mutations in Taiwan.
Materials and Methods: Consecutive adult patients treated with differentiated thyroid cancer between 2017 and 2019 were included in this study. Mutational testing for the TERT promoter was performed by DNA-based polymerase chain reaction.
Results: Among 389 patients included in the analysis, 22 (5.7%) had papillary or follicular thyroid cancer harboring TERT promoter mutations, including C228T (n = 18), C250T (n = 3), and CC242TT (n = 1). The frequency of BRAF V600E mutation was 73%. TERT promoter mutations were significantly associated with older age, tall cell variant of papillary thyroid cancer, extrathyroidal extension, positive surgical margins, lymphovascular invasion, perineural invasion, and distant metastasis. The generalized additive model showed that patient age was positively and almost linearly correlated with the likelihood of the presence of TERT promoter mutations.
Conclusion: The frequency of TERT promoter mutations is relatively low in patients with differentiated thyroid cancer in Taiwan. These tumors carry unfavorable clinicopathologic features, present in a more advanced stage, and probably predict worse prognosis.

Keywords: Age, telomerase reverse-transcriptase promoter mutation, thyroid carcinoma


How to cite this article:
Lai HF, Kuo CY, Cheng SP. Significance of telomerase reverse-transcriptase promoter mutations in differentiated thyroid cancer. Formos J Surg 2021;54:171-6

How to cite this URL:
Lai HF, Kuo CY, Cheng SP. Significance of telomerase reverse-transcriptase promoter mutations in differentiated thyroid cancer. Formos J Surg [serial online] 2021 [cited 2021 Nov 28];54:171-6. Available from: https://www.e-fjs.org/text.asp?2021/54/5/171/327884




  Introduction Top


Thyroid cancer is the most common endocrine malignancy. It ranked as the eighth most common cancer with an age-adjusted incidence of 13.09/100,000 Taiwanese according to the annual report of the Taiwan Cancer Registry in 2017.[1] The majority of newly diagnosed cases were differentiated thyroid cancers. Specifically, papillary and follicular carcinoma constitutes about 92% and 5% of the cases respectively. Differentiated thyroid cancer generally carries an excellent prognosis, with 5-year survival rates of 90.2% in 1997 and 92.4% in 2010.[2] However, locoregional recurrence is not uncommon and exerts a negative impact on the overall survival of patients with thyroid cancer.[3]

The genomic landscape of thyroid cancer has been increasingly elucidated in recent years. BRAF V600E mutation is the most common genetic mutation in papillary thyroid cancer, while RAS mutations are the most common oncogenic driver in follicular thyroid cancer.[4] During the process of tumor progression and dedifferentiation, enrichment of TP53 and TERT promoter mutations are observed.[5] TERT encodes the reverse transcriptase component of telomerase, which facilitates cell proliferation. A few studies have shown that TERT promoter mutations, albeit rare in differentiated thyroid cancer, are associated with aggressive thyroid tumor characteristics.[6] Nonetheless, the frequency and features of TERT promoter-mutant differentiated thyroid cancer have not been systemically analyzed or reported in Taiwan. In this study, we aimed to characterize the clinicopathologic biology of differentiated thyroid cancer harboring TERT promoter mutations at a single tertiary referral center.


  Materials and Methods Top


The study was conducted in accordance with the Declaration of Helsinki and was approved by the institutional review board of our institution (20MMHIS032e). The requirement for informed consent was waived by the review board.

A retrospective review of a prospectively maintained patient database was conducted to identify patients who were treated for differentiated thyroid cancer between 2017 and 2019. Patients who were younger than 20 years and those who had a diagnosis of noninvasive follicular thyroid neoplasm with papillary-like nuclear features were excluded from the study.

The pathologic diagnosis of differentiated thyroid cancer was based on the current diagnostic criteria of the World Health Organization.[7] Tumor-node-metastasis (TNM) staging was classified using the eighth American Joint Committee on Cancer staging system for differentiated thyroid cancer.[8] For papillary thyroid cancer, additional prognostic information was obtained by calculating the scores of metastasis, age, completeness of resection, invasion, and size (MACIS), which was developed by the Mayo Clinic and widely adopted as a risk stratification tool.[9] The risk of recurrence was estimated according to the dynamic risk assessment scheme proposed and recently revised by the American Thyroid Association (ATA).[10]

In our institution, BRAF V600E mutation was determined by Sanger sequencing.[11] Mutational testing for the TERT promoter was performed by polymerase chain reaction (PCR) using genomic DNA extracted from archival formalin-fixed, paraffin-embedded tissue sections. The forward primer was 5'-CAGCGCTGCCTGAAACTC-3' and the reverse primer was 5'-GTCCTGCCCCTTCACCTT-3'.[12] In our preliminary testing, the limit of detection was found to be 15%–20% mutant alleles. Positive and negative controls were included in each assay as quality control.

Results are expressed as mean ± standard deviation or number (percentage). Clinical and pathologic characteristics were compared between groups using the Chi-square test, Fisher's exact test, or Cochran-Armitage trend test for categorical variables.[13] The Student's t-test was used to compare continuous variables between patients with and without TERT promoter mutations. A semiparametric regression approach, the generalized additive model (GAM), was used to evaluate the effects of the patients' age on the probability of TERT promoter mutations.[14] P < 0.05 was considered statistically significant. All analyses were performed using Stata statistical software version 14.0 (StataCorp, College Station, TX, USA).


  Results Top


A total of 396 patients with differentiated thyroid cancer diagnosed between 2017 and 2019 fulfilled the inclusion criteria. Seven patients had no information about the mutational status of the TERT promoter because of technical issues (low DNA extraction yield or poor DNA quality). These patients were excluded from further analysis. In all, 389 patients comprised the study cohort.

The mean age of the study cohort was 48 ± 13 years, and 300 (77%) were women. Hashimoto thyroiditis and Graves disease were present in 90 (23%) and 15 (4%) of the patients respectively. Twenty-two (5.7%) patients had thyroid cancer harboring TERT promoter mutations [Figure 1], including C228T (n = 18), C250T (n = 3), and CC242TT (n = 1). As shown in [Table 1], patients who had TERT promoter mutations were significantly older. TERT promoter mutations were also associated with shorter stature. Nonetheless, it likely reflected the fact that body height was negatively correlated with age (r = −0.418, P < 0.001 by linear regression).
Figure 1: Schematic illustration showing the telomerase reverse-transcriptase promoter region with cancer-specific telomerase reverse-transcriptase promoter mutations. Highly recurrent C >T mutations create de novo transcription factor binding sites (not precisely scaled). The figure adapted medical elements from Servier Medical Art templates (https://smart.servier.com/) licensed under a Creative Commons Attribution 3.0 Unported License (https://creativecommons. org/licenses/by/3.0/).

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Table 1: Demographics of 389 patients with differentiated thyroid cancer stratified by the mutational status of telomerase reverse transcriptase promoter


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The majority (368/389, 95%) of the patients had papillary thyroid cancer. In our study cohort, only 27% were microcarcinomas ≤1 cm in the greatest dimension. About 8% (31/368) were nonclassic, nonfollicular rare variants. The majority were of high biological aggressiveness according to the 2017 World Health Organization classification,[7] such as tall cell variant (n = 16) and diffuse sclerosing variant (n = 7). Interestingly, the frequency of TERT promoter mutations was higher in these aggressive variants. Moreover, the size of these thyroid cancers with TERT promoter mutations was significantly larger than those without mutations (mean tumor size, 2.9 ± 2.1 cm vs. 1.7 ± 1.2 cm). The presence of TERT promoter mutations was also associated with several unfavorable pathologic features, including extrathyroidal extension, positive surgical margins, lymphovascular invasion, perineural invasion, and distant metastasis [Table 2].
Table 2: Pathologic features of 389 patients with differentiated thyroid cancer stratified by the mutational status of telomerase reverse transcriptase promoter


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The rate of BRAF V600E mutation was 73% (284/389), consistent with the prevalence rate found in previous reports in Taiwan.[15],[16] BRAF V600E mutation was not associated with TERT promoter mutations, irrespective of tumor type. Of note, 18 (82%) had dual mutations.

For papillary thyroid cancer, tumors harboring TERT promoter mutations had significantly higher MACIS scores [Table 3]. In addition, tumors positive for TERT promoter mutations had more advanced TNM staging. Based on the ATA risk estimate of recurrence, about 77% of the tumors with TERT promoter mutations had a high risk of recurrence.
Table 3: Staging of 389 patients with differentiated thyroid cancer stratified by the mutational status of telomerase reverse transcriptase promoter


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We found that old age was the main predictor of TERT promoter mutations. The youngest patient who had differentiated thyroid cancer harboring TERT promoter mutations was 42 years old, and only 4 (18%) patients with TERT promoter mutations were younger than 55 years. We performed a GAM analysis adjusted for sex and tumor type. As shown in [Figure 2], the age at diagnosis was positively and almost linearly correlated with the likelihood of the presence of TERT promoter mutations.
Figure 2: Odds ratio of telomerase reverse-transcriptase promoter mutations versus age at diagnosis in patients with differentiated thyroid cancer, adjusted for sex and tumor type. The dashed lines represent the 95% confidence intervals

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  Discussion Top


In this study, we determined the mutational status of the TERT promoter in our patient cohort. Recurrent somatic mutations in the TERT promoter in thyroid cancer were initially reported in 2013.[17] Normal thyroid tissue or benign lesions do not harbor TERT promoter mutations. Subsequently, the frequency of TERT promoter mutations in differentiated thyroid cancer was found to vary substantially among studies. In a recent review, the average frequency of TERT promoter mutations was 11% and 17% in papillary and follicular thyroid cancer respectively.[6] High mutation frequency was detected in Latino and Japanese patients,[18],[19] while relatively low frequency of 5.7% in this study was similar to those reported in Korean and Chinese patients.[20],[21] The frequency appears mainly affected by the patient demographics and tumor characteristics. For instance, the average tumor size was 2.35 cm in the Colombian study and 0.7 cm in the Korean study respectively.[18],[20] The referral pattern and feasibility to health care services probably played a more important role than ethnicity.

In agreement with previous reports,[6] we found that TERT promoter mutations in differentiated thyroid cancer were associated with aggressive clinicopathologic features, such as tall cell variant of papillary thyroid cancer, extrathyroidal extension, lymphovascular invasion, and distant metastasis. In this study, the prevalence of TERT promoter mutations in tall cell variants of papillary thyroid cancer was 25% (4/16). In addition, TERT promoter mutations might be an independent predictor of lymphovascular invasion.[22] In contrast, the influence of TERT promoter mutations on lymph node metastasis was less consistent.[6] The discrepancy may result from different surgical strategies of performing prophylactic central neck dissection. In our institution, we routinely performed ipsilateral central compartment dissection on the affected side.[23] An updated meta-analysis showed that prophylactic central neck dissection significantly reduced locoregional recurrence but might increase operative complications in inexperienced hands.[24]

We confirmed that TERT promoter mutations were highly prevalent (5/7, 71%) in patients with distant metastasis. A recent study showed that TERT promoter mutations were enriched in advanced thyroid cancer with distant metastasis, and high concordance was observed between the primary tumor and metastatic sites.[25] Transcriptome analysis disclosed that molecular pathways involving DNA damage responses and cell cycle regulation were upregulated in papillary thyroid cancer with TERT promoter mutations.[26] These findings suggested that TERT promoter mutations not only confer proliferative advantages to thyroid cancer cells but also heighten their invasive and metastatic capacity. Furthermore, TERT promoter mutations were associated with radioactive iodine refractory state in papillary thyroid cancer.[27] Given that the disease-free survival of patients with TERT promoter mutations tended to be shorter in patients undergoing lobectomy compared to total thyroidectomy,[19] we proposed that more aggressive treatment strategies (total thyroidectomy plus prophylactic central neck dissection) should be considered if the presence of TERT promoter mutations in thyroid cancer was detected preoperatively.

Other than molecular techniques, predicting the occurrence of TERT promoter mutations in thyroid cancer was difficult. Several ultrasonographic features including taller-than-wide shape, microlobulated margin, and capsule contact or involvement were associated with TERT promoter mutations.[28] In this study, we demonstrated that patient age was a key predictor of TERT promoter mutations. Our observation that TERT promoter mutations were more common in elderly patients was in line with other studies.[6] Conversely, TERT promoter mutations were hardly seen in pediatric and young adult patients with differentiated thyroid cancer.[29] Notably, TERT promoter mutations were commonly seen in tissues with relatively low rates of self-renewal, which had low telomerase activity.[30] When proliferation rate increased due to oncogenic drivers in tumor cells arising from these tissues, telomeres gradually shortened and a critical telomere length was more readily reached in elderly patients. Eventually, selection pressure from the telomere crisis led to the acquisition of TERT promoter mutations and induction of aggressive phenotype in tumor cells.

The increase in cancer cell proliferation and the resultant selection pressure might be independent of the initial oncogenic driver. In this study, we did not detect associations between BRAF V600E mutation and TERT promoter mutations. Earlier studies suggested a positive association between the two mutation events, but the relationship was not consistent.[6] It may be influenced by the frequency of either mutation. In agreement with our findings, studies with a low frequency of TERT promoter mutations and a high prevalence of BRAF V600E mutation generally reported an absence of the association between the two mutation events.[20],[21]

In conclusion, the frequency of TERT promoter mutations is relatively low among patients with differentiated thyroid cancer in Taiwan. Nonetheless, tumors harboring TERT promoter mutations carry unfavorable clinicopathologic features, present in a more advanced stage, and probably predict a worse prognosis. Patients with known TERT promoter mutations may need aggressive initial treatment and close surveillance for recurrence.

Financial support and sponsorship

This work was supported by research grants from the Ministry of Science and Technology of Taiwan (MOST-107-2314-B-195-001-MY3) and MacKay Memorial Hospital (MMH-11008).

Conflicts of interest

There are no conflicts of interest.



 
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30.
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