Telomerase related studies in thyroid cancer

Follicular thyroid neoplasms are diagnostically challenging. On histologic evaluation, it can be difficult, resource-consuming, and observer-dependent to pinpoint the exact location of capsular or vascular invasion. In some cases, it is impossible to do so unequivocally – for those, the term “follicular tumor of uncertain malignant potential” (FT-UMP) was created. On cytologic evaluation, it is less challenging but rather hardly possible to distinguish follicular thyroid adenoma (FTA) from follicular thyroid carcinoma (FTC). With the advent of molecular analyses in clinical diagnostic settings, many mutational events have been associated with specific cancers. Amongst those, two point mutations in the TERT promoter region, named C228T and C250T have been of particular interest as they have been associated with malignant properties in thyroid tumors in general and a worse prognosis with a higher frequency of relapse in particular.

This thesis aims to improve the diagnostic accuracy for thyroid tumors in general and for follicular thyroid tumors in particular through the implementation of TERT promoter mutational screening. Study I evaluates the role of TERT promoter mutational screening in a clinical series of FT-UMPs and how this analysis aids in detecting relapse-prone tumors. This could help alter adjuvant treatment modalities even in the absence of clearcut histopathological evidence of malignant potential.

Study II shows that digital droplet PCR (ddPCR) can improve the sensitivity for the detection of TERT promoter mutations in follicular thyroid tumors and can even detect TERT promoter mutations when they occur subclonal and are heterogeneously distributed in FT-UMPs.

Study III validates TERT promoter mutational testing on preoperative material in the form of frozen pellets from thyroid FNAC material. We were able to show that ddPCR is a reliable analysis for cytologic material and may help to identify high-risk cases and triage them to a more aggressive treatment plan up-front, underlining the markers' diagnostic and prognostic value.

Study IV tries to evaluate 5hmC immunoreactivity as an expressional analysis to pinpoint TERT promoter mutations in FTCs. Even though the study was able to show that the loss of 5hmC immunoreactivity may signify TERT promoter mutations in subsets of FTCs, we could not prove its clinical value to predict the TERT promoter mutational status. Further studies are therefore warranted.

In summary, the findings in this thesis highlight the clinical importance of TERT promoter mutational screening in follicular thyroid neoplasms. Furthermore, we were able to show that ddPCR is a reliable technique for interrogating specific mutations of the TERT promoter.

List of scientific papers

I. Hysek M, Paulsson JO, Jatta K, Shabo I, Stenman A, Höög A, Larsson C, Zedenius J, Juhlin CC. Clinical Routine TERT Promoter Mutational Screening of Follicular Thyroid Tumors of Uncertain Malignant Potential (FT-UMPs): A Useful Predictor of Metastatic Disease. Cancers (Basel). 2019 Sep 26;11(10):1443.
https://doi.org/10.3390/cancers11101443

II. Hysek M, Jatta K, Hellgren LS, Stenman A, Larsson C, Zedenius J, Juhlin CC. Spatial Distribution Patterns of Clinically Relevant TERT Promoter Mutations in Follicular Thyroid Tumors of Uncertain Malignant Potential: Advantages of the Digital Droplet PCR Technique. J Mol Diagn. 2021 Feb;23(2):212-222.
https://doi.org/10.1016/j.jmoldx.2020.10.016

III. Hysek M., Hellgren LS, Stenman A, Darai-Ramqvist E, Ljung E, Schliemann I, Condello V, Larsson C, Zedenius J, Jatta K, & Juhlin CC. Digital droplet PCR TERT promoter mutational screening in fine needle aspiration cytology of thyroid lesions: A highly specific technique for pre-operative identification of high-risk cases. Diagnostic cytopathology. 2023 Mar 4.
https://doi.org/10.1002/dc.25120

IV. Hysek M, Hellgren LS, Condello V, Larsson C, Zedenius J, Juhlin CC. 5hmC immunohistochemistry: a predictor of TERT promoter mutational status in follicular thyroid carcinoma? Journal of Histochemistry & Cytochemistry. 2023;71(8):451-458.
https://doi.org/10.1369/00221554231190437