Medullary carcinoma arising in a thyroid with Hashimoto's disease.

A 51-year-old woman presented with a large goiter and on pathologic examination was found to have both Hashimoto's thyroiditis and medullary carcinoma of the thyroid. To our knowledge, this is the first well-documented case of the coexistence of these two entities in the same patient in the English literature. The association of Hashimoto's disease and carcinoma of the thyroid is reviewed and its relevance discussed.