Malignant Thyroid Disease

The wide spectrum of aggressiveness of thyroid cancer is extra-ordinary, ranging from differentiated malignancies in which most patients live out close to their normal lifespan to anaplastic varieties that are almost universally lethal. Most thyroid tumors arise from the follicular cells, and most are well-differentiated (papillary and follicular). Poorly differentiated (insular) and undifferentiated (anaplastic) types are rare. Hürthle cell neoplasms (Ashkenazy cell or Langhans tumors) are an uncommon and generate much controversy regarding their cell of origin (follicular versus para-follicular) and their pathological nature (benign versus malignant). Medullary thyroid carcinomas are neuroendocrine neoplasms derived from the para-follicular cells (C-cells) and account for 5% of thyroid neoplasms. Thyroid lymphomas comprise <5% of thyroid malignancies and 2% of all lymphomas; the majority are non-Hodgkin’s lymphomas of B-cell origin. The most common primary tumors that metastasize to the thyroid gland are carcinomas of the kidney, lung, colon, and melanoma. Sometimes, thyroid cancer infiltrates into structures in the neck such as the trachea, esophagus, blood vessels, muscles, or nerves. Thyroid cancer may metastasize to lymph nodes, lungs, bone, and occasionally brain. Fortunately, metastases will often take up iodine and respond well to radioactive iodine therapy. This chapter discusses the risk factors, pathology, clinical presentation, diagnosis, staging, treatment, and prognosis of the different types of thyroid cancer.