TERT promoter mutational screening as a tool to predict malignant behaviour in follicular thyroid tumours-three examples from the clinical routine.

Follicular thyroid adenomas (FTAs) and carcinomas (FTCs), collectively the most common thyroid neoplasms, constitute a significant clinical challenge since histological evidence of invasive behaviour is required for a malignant diagnosis. Small subsets of FTAs relapse as manifest malignant FTCs, indicating that histology is not always adequate to predict malignant potential. Lately, recurrent mutations in the promoter of the Telomerase reverse transcriptase (TERT) gene have been coupled to FTCs, whereas FTAs usually lack this aberrancy. We describe three patients with follicular thyroid tumours in which TERT promoter mutational screening was employed as part of the clinical work-up to pinpoint malignant potential. In two retrospective analyses of seemingly benign lesions, the detected mutations predicted future skeletal metastases, and in one prospective case, the mutational screening led to a different clinical management of the afflicted patient. We therefore consider TERT promoter mutational screening an adjunct tool of value in equivocal cases.