Primary hypothyroidism in breast cancer patients with irradiated supraclavicular lymph nodes.

Since the treatment of postmenopausal breast cancer patients with aminoglutethimide caused hypothyroidism with an unexpectedly high frequency previous treatment was suspected to contribute to hypofunction of the thyroid. Serum thyrotropin, triiodothyronine and free thyroxine index were compared between breast cancer patients who had undergone irradiation of regional lymph nodes and non-irradiated breast cancer patients, as well as patients having endometrial or colorectal carcinoma. Subclinical and clinical primary hypothyroidism was significantly more frequent in breast cancer patients who had previously received irradiation on supraclavicular lymph nodes comprising a minor part of the thyroid. Testing for the presence of autoantibodies against thyroid tissue components gave no evidence for radiation-induced autoimmune thyroiditis. Drugs suppressing thyroid hormone synthesis like aminoglutethimide may frequently cause myxedema in such irradiated women, especially at postmenopausal age.