A population of 5,266 persons were known to be at risk for the development of thyroid neoplasms as a result of prior head and neck irradiation for benign conditions received at our institution. We contacted 2,578 (49.0 per cent) of these persons of whom we examined 1,476 (28.0 per cent) and received follow-up data on 713 (13.5 per cent). Prior to the onset of our recall program, 209 persons had had thyroid surgery (9.4 per cent of those with adequate follow-up data). The incidence of thyroid operations after the initial radiation treatment was low for 10 years and then increased continuously for at least 25 years. The incidence of carcinoma found at operations performed before the recall program and after was similar (37.1 per cent before versus 36.2 per cent after). This high percentage, which was not changed by the follow-up and examination program, supports the conclusion that the probability of finding thyroid cancer in a nodular gland is increased in irradiated patients. No risk factors were found in irradiated subjects that distinguished between malignant and benign disease. Of 50 patients who were examined and who had a history of prior thyroid surgery, 18 (36 per cent) had evidence of new thyroid tumors. In this limited group, thyroid suppressive therapy appeared to prevent recurrences. However, a larger trial to assess the value of thyroid suppression is still warranted. One subject is known to have died of thyroid cancer.
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