Unusual types of thyroid neoplasms.

This article discusses several unusual forms of primary thyroid neoplasms. The TCV of PTC and insular thyroid carcinoma appears to have a more aggressive clinical behavior than DTC in most patient groups and may respond to thyroid hormone suppression and radioiodine. Anaplastic thyroid carcinoma, which may develop from differentiated thyroid tumors, has a poor prognosis which may be altered by surgery and radiation therapy but not typically by radioiodine and thyroid hormone suppression. Primary squamous cell carcinoma of the thyroid is an unusual entity that may be associated with a clinical syndrome that includes leukocytosis, fever, and hypercalcemia. Primary thyroid lymphoma is frequently associated with Hashimoto's thyroiditis and should be considered especially in older patients with rapidly enlarging thyroid masses. Although there are no studies assessing this issue, it seems reasonable that patients who have undergone thyroidectomy for neoplasms of thyroid cells that are poorly differentiated and do not concentrate radioiodine (e.g., squamous cell, anaplastic) should receive sufficient thyroid hormone suppression, if tolerated, to reduce TSH (third-generation assay) to approximately 0.1 to 0.3 mu U/mL, because TSH may be a growth factor. If, however, the tumor concentrates or responds to radioiodine, suggesting more differentiated cells (e.g., TCV, insular carcinoma), the target TSH level (third-generation assay) should range from 0.01 to 0.1 mu U/mL, as tolerated. Patients with primary thyroid neoplasms arising from cells other than thyrocytes (e.g., lymphoma) can be maintained at a TSH level of 0.5 to 1.5 mu U/mL. Our conclusions and analyses are often based upon small, retrospective, poorly controlled reports, and further studies are required to allow a better understanding of the evaluation and treatment of these neoplasms.