TERT promoter mutations are rare in parathyroid tumors.

The majority of parathyroid tumors are benign, and parathyroid carcinomas represent a diagnostic challenge with limited treatment options. Multiple endocrine neoplasia type 1 gene and cell division cycle 73 (CDC73) are major genes in parathyroid adenomas and carcinomas respectively. However, a large group of parathyroid tumors remain without defined genetic background. Telomeres are chromosome-capping structures designed to protect DNA integrity. During mitosis, the telomere repeats are gradually shortened, which limits the number of possible cell divisions. In order for cancer cells to escape senescence, alterations in telomere maintenance are required. The telomerase reverse transcriptase (TERT) gene encodes the catalytic subunit of the telomerase complex and is largely responsible for maintaining the telomere length. Mutations in the promoter of the TERT gene may cause alterations in transcription factor binding sites, which leads to TERT overexpression and telomerase activation, as was first described for melanoma (Horn et al. 2013). Recently, the common TERT promoter mutations -146COT (also called C250T) and -124COT (C228T) have been implicated in the development of several endocrine tumors. They have been identified in papillary, follicular, and anaplastic carcinomas of the thyroid, adrenocortical carcinomas, and paragangliomas. Interestingly, the mutations were found to be associated with telomerase activation, telomere length, malignant disease, patient age, and adverse prognosis (Liu et al. 2014). In addition to the potential prognostic value, the ongoing development of telomerase inhibitors for clinical use could provide additional treatment options for patients with aggressive endocrine cancer. Previous studies have identified telomerase activity as well as TERT gene expression in parathyroid carcinomas but not in adenomas or normal parathyroid tissue (Falchetti et al. 1999, Kammori et al. 2003). Additionally, the telomerase inhibitor azidothymidine was able to