Hashimoto's thyroiditis and breast cancer.

The question of a possible association between Hashimoto's thyroiditis and breast cancer was evaluated in (1) an autopsy series and (2) a follow-up of a cohort of patients with Hashimoto's thyroiditis at the Mayo Clinic. In the autopsy study, 174 subjects with histologic diagnosis of Hashimoto's thyroiditis were matched with a control group. There was no significant difference in the frequency of a history of breast cancer in the two groups. In the cohort of Olmsted County residents with a clinical or histologic diagnosis of Hashimoto's thyroiditis for whom there was a substantial period of follow-up, no excess frequency of breast cancer was note. These results contrast with those of a recent study reporting that Japanese women with Hashimoto's thyroiditis were a high risk group for breast cancer.