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Pathology of thyroid cancer 

Pathology of thyroid cancer
Chapter:
Pathology of thyroid cancer
Author(s):

Yolanda C. Oertel

DOI:
10.1093/med/9780199235292.003.3329
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date: 16 November 2019

The majority of thyroid cancers arise from the follicular epithelium, are usually well differentiated, and thus many have a follicular architecture with varying amounts of colloid present. Medullary carcinoma constitutes a minority of thyroid cancers and arises from the C cells.

Fine-needle aspiration (FNA) biopsy is the accepted diagnostic test to determine whether a thyroid nodule is benign or malignant (1, 2). The role of the cytopathologist in the interpretation of smears has been considered crucial, and I believe this is partially valid. Based upon 30 years of experience as an ‘interventional pathologist’ who performs and interprets many aspirates, I emphasize that the quality of the sample is the crucial factor. The pathologist’s interpretation is only as good as the sample he/she obtains or receives, and not enough attention has been paid to the technique of aspiration. I have trained numerous physicians to perform FNAs in a skilful fashion in a short period of time, and I refer the reader to my previous publications (3–5). The high rate of ‘unsatisfactory specimens’ reported in the literature is concerning. This was discussed at the National Cancer Institute Thyroid Fine-Needle Aspiration State of the Science Conference in October 2007 (6) and it was recommended that ‘at the end of training and for re-credentialing 90% diagnostic samples should be documented’. Please note that FNA biopsy should not be confused with needle biopsies (e.g. Tru-cut, Vim-Silverman, etc.) that yield tissue fragments that are processed for histological diagnosis.

The usual classification of thyroid cancers is founded on their histological and cytological features, many of which have been correlated with the clinical behaviour of the tumours. In addition, the age of the patients and the extent of the tumours are particularly important to determine the prognosis. The classification I follow is that of the WHO (7) with some of the modifications by the Armed Forces Institute of Pathology (AFIP) (8). My discussion will be focused largely on the most common types (see Box 3.5.5.1). Prolonged follow-up of the patients and extensive modern studies of the tumours indicate that papillary carcinomas and follicular carcinomas have histological similarities and are usually of a low grade of malignancy, but they also have a variety of inherent differences.

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