Tall Cell Variant of Papillary Thyroid Carcinoma

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Abstract
Papillary thyroid carcinoma is the most common endocrine malignancy and the most common malignant tumor of the thyroid gland. The majority of papillary carcinomas enjoy an excellent short-term and long-term prognosis with most patients surviving decades even in the presence of regional lymph node metastases. Occasional patients will demonstrate distant metastases usually to the lungs and this may present as lymphangitic spread or hematogenous metastasis. Less usual sites of distant metastases include bone, brain and liver. Over the past 20 years a number of variants of papillary carcinoma have been described and their clinical and pathologic features reported. Many of these variants are histological curiosities and from a clinical standpoint do not impact patient prognosis or quality of life. Other variants are important to recognize because of their associations with non-thyroidal lesions; the best example of this is cribriform-morular variant which is associated with familial adenomatous polyposis of the colon. Some types of papillary carcinoma are reportedly more aggressive than classic type. The one most frequently referred to in this regard is the tall-cell variant of papillary carcinoma. Originally described in 1976 by the group from the Cleveland Clinic as a particularly aggressive thyroid cancer, several series have appeared in the literature which have recognized its clinical behavior. Unfortunately the pathologic definition of tall-cell variant has not been uniform. It should be defined by its cellular characteristics; these include abundant cytoplasm, which is often eosinophilic although not granular and the nucleus which is elongated and stratified cell to cell. The nuclei can but not necessarily always show all of the features of the so-called papillary carcinoma nucleus. Controversy has existed with regard to the amount of cytoplasm present and the configuration of the cell. In the 2004 WHO classification of endocrine neoplasms, tall-cell papillary carcinoma cells should be 2 times as tall as they are wide. In many examples of this carcinoma this definition is exceeded. The pattern of growth of these lesions is frequently very papillary, and in some examples this is so florid as to assume a trabecular growth pattern. It is uncommon to see follicular differentiation in this tumor. The question that also has been controversial is "how much of a thyroid cancer should show the tall-cell pattern to be diagnosed as tall-cell variant?" Some authors have claimed 10%, 30%, or 70%. Again from the WHO classification, it should be at least 50%. In my experience tall-cell papillary carcinomas are frequently totally tall-cell in pattern.

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