Metastatic Tumors, Lymphomas, and Rare Tumors of the Thyroid

Metastatic tumors to the thyroid gland and direct extension to the thyroid from an adjacent malignancy are uncommon. The tumors that most often metastasize to the thyroid are cancers of the lung, breast, skin (especially melanoma), colon, and kidney. In rare cases, the thyroid metastasis is the initial clinical presentation of the malignancy. With routine and special stains, the distinction from a primary neoplasm of the thyroid is often achievable with fine needle aspiration (FNA). Malignant lymphomas occur as primary malignancies of the thyroid, but they can also involve the thyroid gland secondarily as a manifestation of systemic disease. Some rare epithelial and mesenchymal neoplasms of the thyroid that have a characteristic cytomorphology and/or distinctive immunoprofile can be recognized and diagnosed by FNA.