Hashimoto's thyroiditis with medullary carcinoma.

The association of Hashimoto's thyroiditis with lymphoma and papillary carcinoma has been recognized, but there have been few reports of an association between Hashimoto's thyroiditis and medullary carcinoma of the thyroid gland, especially in Canada. The authors report three cases, seen in an 18-month period, of Hashimoto's thyroiditis and medullary carcinoma in patients whose relatives had multiple endocrine neoplasia type II. The findings support the view that the thyroiditis occurred in response to the tumour process and not vice versa.