Hashimoto's thyroiditis and carcinoma of the thyroid gland.

Seven cases of Hashimoto's disease (HT) occurring in association with carcinoma of the thyroid gland are presented. The diagnosis of HT was not reached before surgery in any of the cases; it was an incidental histopathological finding. There was no case of pure papillary cancer: two specimens showed mixed papillary and follicular cancers, four revealed follicular carcinomas (one of them with anaplastic areas) and one medullary neoplasm. Other authors, however, have reported that pure papillary carcinoma occurred with significantly greater frequency in thyroids also displaying Hashimoto's disease. Total thyroidectomy was performed in all seven patients and one patient with anaplastic follicular cancer also received external irradiation. TSH suppressive therapy was given postoperatively. All these patients are alive with no evidence of further disease after seven to 17 years of follow-up study, whereas the mortality in our total series of thyroid cancers, even in patients with low-grade malignancy, was about 9%. Thus the prognosis of patients with carcinoma of the thyroid gland with coexisting Hashimoto's disease is better than that of patients with carcinoma of the thyroid gland alone. Hashimoto's thyroiditis does not seem to be a premalignant lesion. There was no evidence suggesting that thyroid carcinoma originated in the proliferating epithelium of Hashimoto's thyroiditis. It would appear that thyroid carcinoma stimulates the development of HT in some patients and that the presence of the autoimmune inflammatory reaction and the circulating antibodies retard growth and dissemination of carcinoma of the thyroid gland.