Neoplasms in Persons Treated With X Rays in Infancy for Thymic Enlargement. A Report of the Third Follow-Up Survey2

Abstract

In upstate New York, 2,878 persons given X-ray treatment in infancy for thymic enlargement and their 5,006 untreated siblings were surveyed by mail in 1963 for the third time to determine the current incidence of neoplasms and mortality. Questionnaires revealed that an excess number of tumors had developed in the treated population since last surveyed (1959). Thyroid neoplasms, including 5 carcinomas, accounted for 11 of the 26 new tumors. No new cases of leukemia or osteochondroma occurred after age 20. A definite dose response was established for both thyroid and “pooled” extrathyroid neoplasms. The incidence of thyroid neoplasms was much higher in persons treated with anterior and posterior (AP) X-ray ports than in those treated with anterior (A) ports only. Presumably, this was because AP treatment usually irradiated the gland with the primary X-ray beam, whereas A treatments usually exposed the gland to smaller doses of scattered X rays. The magnitude of the thyroid dose could not be correlated with (a) the latent period between exposure and tumor development, or (b) whether any given lesion was malignant or benign. The incidence curve for thyroid neoplasms rises sharply in the 10–19 year category, flattens in the 20–29 year category, and that for carcinomas may actually decline after age 20. Five of the six thyroid carcinomas occurring under age 15 were in males. All 19 persons with thyroid carcinomas, including 9 with metastases, responded well to therapy and were healthy at the time of survey. Plans for future study of the high-risk and low-risk groups in the irradiated population are discussed.