Pathology and Classification of Thyroid Tumors

Nodules of the thyroid gland are common and frequently problematic specimens encountered by the diagnostic surgical pathologist. It is estimated that 4–7% of adults have a palpable thyroid nodule, and several times that many have nodules which are detectable at autopsy or by ultrasound. Of the estimated 10–20 million clinically detectable thyroid lesions in the United States, approximately 5–30% will be malignant. Thyroid nodules are more common in women, in people with a history of radiation exposure, and in those with goitrogenic-rich diets or iodine-deficient diets (Faquin, Arch Pathol Lab Med 132:622–632, 2008). Carcinomas of follicular cell origin are the most common and greatly outnumber carcinomas of C-cell origin. Secondary malignancies and lymphomas are far less common than follicular origin tumors, but they do occur and must be considered in the differential diagnosis of both benign and malignant thyroid abnormalities. The majority of carcinomas of follicular origin are indolent, with approximately 90% 10-year survival rates.