Thyroid Neoplasms following Irradiation*

Animal experiments and clinical observations have demonstrated that carcinoma of the thyroid may follow irradiation of the gland. In rats, thyroid carcinomas with metastases have been produced by the administration of 131 (Goldberg and Chaikoff, 1952). If the radioactive iodine or x-irradiation is given with a goitrogen, the tumours are more readily produced and a smaller dose of irradiation is effective (Doniach, 1958). Exposure of the human thyroid gland to ionizing radiation has become increasingly frequent. The isotopes $'lI and 1321 are widely used in the diagnosis of thyroid disorders, and the former is also employed extensively-in the treatment of thyrotoxicosis. In the past, before radioiodine was available, this condition was sometimes treated by x-irradiation. Treatment of cutaneous lesions in the neck with radium or x rays may lead to some incidental irradiation of the thyroid gland. In some centres it was the practice to irradiate enlarged thymus glands in infancy, and this procedure also inevitably involved the thyroid gland. There are several reports of carcinoma of the thyroid in man developing after irradiation. It has only rarely been reported after the treatment of thyrotoxicosis by x-irradiation (Quimby and Werner, 1949). The findings in children have been of greater significance, and there is now a well-recognized association between irradiation of the cervical and upper thoracic region in infancy and the subsequent appearance of a carcinoma of the thyroid (Duffy and Fitzgerald, 1950; Clark, 1955 Fetterman, 1956; Simpson and Hempelmann, 1957). In view of the increasing use of radioactive materials, information regarding the development of carcinoma of the thyroid gland following irradiation, either deliberate or accidental, is clearly important. In a previous report three patients who developed carcinomas in these circumstances were briefly described (Kilpatrick, Blomfield, Neal, and Wilson, 1957). Six further patients have now come under observation; in four the diagnosis of carcinoma was clearly established, and in two there was an adenomatous condition of the thyroid presenting some neoplastic features, though a firm diagnosis of carcinoma was not possible. These cases are now reported in detail.