Thyroid carcinoma in man after exposure to ionizing radiation. A summary of the findings in Hiroshima and Nagasaki

Patterns of human thyroid parenchymal reaction following low-dose childhood irradiation

Microscopic changes in the thyroids of 68 patients who had received low-dose childhood irradiation to the head and neck and who presented with palpable thyroid abnormalities culminating in surgery are compared to 34 control thyroids obtained from age- and sex-matched autopsy cases. Eighty-eight percent of irradiated thyroids showed moderate to severe focal hyperplasia, 51% contained single or multiple adenomas or adenomatous hyperplastic nodules, 68% exhibited chronic lymphocytic thyroiditis, 51% revealed colloid nodules, 42% presented with oxyphile change, 25% had mild fibrosis and 59% contained well-differentiated papillary, follicular or mixed thyroid carcinoma averaging 1.6 cm in diameter. Three small carcinomas were of the sclerosing type. The non irradiated thyroids showed 32% colloid nodule formation, 17% focal hyperplasia, 6% adenomatous hyperplasia and no identifiable carcinomas. Several nonspecific histologic abnormalities are now recognized as following low-dose radiation to the thyroid, the most important being focal hyperplasia, which may represent a pre-malignant change in thyroid parenchyma.

Salivary gland tumors in atomic bomb survivors, Hiroshima, Japan. I. Epidemiologic observations

An epidemiologic investigation was undertaken in Hiroshima to study the relationship of salivary gland tumors to exposure to ionizing radiation. Two hundred and eleven cases examined between 1953-1971 were confirmed by a review of histologic specimens. Of these, 66 cases occurred in residents of Hiroshima City who were born before the A-bomb: 30 among A-bomb-exposed, and 36 in non-exposed individuals. The incidence of salivary gland tumors among the exposed individuals was significantly higher, 2.6 times greater than that among the nonexposed individuals for all tumors, and 10 times greater for malignant tumors. The incidence increased with proximity to the hypocenter for the directly exposed. An increased incidence was also found among early entrants, particularly those entering the city within 3 days of the A-bomb.

The relationship of head and neck irradiation to the subsequent development of thyroid neoplasms

Individuals who have received head and neck radiation for benign conditions have a markedly increased risk of developing thyroid, salivary, and perhaps breast cancer as compared to the general population. Although the relative risk is very high, the absolute risk that any one individual who has had head or neck irradiation will develop a subsequent malignancy is low. Identification of these patients through some type of screening procedure may be beneficial in terms of prevention of subsequent morbidity and perhaps mortality from cancer, especially thyroid and salivary cancer. The risks of any detection or prophylaxis program must be carefully weighed against the probable, but unproved benefits of early detection. A major unresolved question is the natural history of microscopic thyroid carcinoma in the 25 yr-40 yr old radiation exposed population.