Endocrine Abstracts

Background: In accordance with the WHO Classification of tumours of endocrine organs (Lyon, 2004) clear cell thyroid lesions have not been separated in one category as they are occurred quite rare, characterized by various cellular origin, heterogeneous morphological type, and malignant potential. Difficulties of morphological diagnosis of clear cell thyroid lesions are also obvious.

Aim: Retrospective morphological study of clear cell thyroid tumours has been performed by pathologists of two research centres (MRRC and ERC) for the period of 10 years (2007–2016) to analyse difficulties of diagnosis related with different histotype, and tumour grade.

Materials and Methods: Histological sections of paraffin blocks from 14 cases of clear cell tumours in 5 male and 9 female aged from 15 to 78 years have been stained with H&E, and immunohistochemistry (IHC) for Thyroglobulin (Tg), Thyroid Transcription Factor 1 (TTF1), Calcitonin (Cal), Chromogranin A (Chr A), Parathyroid Hormone (PTH), CD10, and Ki-67.

Results: Retrospective review of H&E and IHC stained sections allows to make diagnosis of 3 benign follicular thyroid adenomas (FTA), 2 follicular thyroid carcinomas (FTC), 3 papillary thyroid carcinomas (PTC), 1 medullary thyroid carcinoma (MTC), 2 poorly differentiated thyroid carcinomas (PDTC) with clear cell features, 2 intrathyroid parathyroid carcinomas (ITPTC), and 1 renal cell metastasis into thyroid (RCC metastasis). Tumour cells of FTA (2 pure clear cell and 1 signet ring cell), FTC, PTC, and PDTC are Tg-, and TTF1-positive, in comparison with negative Cal-, Chr A-, PTH-, CD10-staining. Ki-67 is expressed by nucleus of more than 30% PDTC tumour cells in comparison with low expression rate (less than 1%) of highly differentiated tumours. Tumour cells of MTC are Tg-, PTH-, and CD10-negative, but positive for TTF1-, Cal-, and Chr A- staining. Cells of ITPTC are Tg-, TTF1-, Cal-, CD10-negative, but Chr A-, and PTH-positive. Cells of RCC metastasis are positive for CD10, but negative for Tg-, TTF1-, Cal-, Chr A-, and PTH.

Conclusions: Clear cell thyroid tumours are rare and should be distinguished in accordance with their different cellular origin and histotype, as well as various tumour grade and prognosis.