ao’ oe Sta tie ae YR a eR ee at ee @ i -~ € Radiation-Associated Thyroid Carcinoma 245 exposure. Subsequently there was continuing development of thyroid nodules in the Rongelap and Ailingnae populations and more recently in the least exposed Utirik population. At present 40 of 243 exposed Marshallese (16.5%) are affected (ratio of females to males affected is 2:1). Table 2 shows the numbers of benign and malignant tumors in the different groups with estimated average thyroid dose and comparison of those exposed at < 10 and > years of age. There appears to be a dose related response, with the greatest incidence of tumors in the Rongelap children (75%). Thyroid surgery has been performed on 31 exposed Marshallese and 3 unexposed \/. The thyroid glands of most of the exposed Rongelap people undergoing surgery contained multiple nodules or areas of adenomatous change. Often those with only one palpable nodule proved to have multiple nodules. Microscopic examina‘tion showed that many of the lesions were surrounded by a capsule and, unlike the remainder of the gland, had distinct histological patterns ranging from microfollicular to fetal, solid, or embryonal types, and many showed hemorrhagic or degenerative changes (6). Adenomatous changes were not unlike those seen in chronic iodine deficiency, except that most of the goiters were smaller in the Marshallese. Many of the glands were found to contain minute lesions, some composed of solid cell masses, which, although conSidered benign, were composed of discrete areas of atypical cells suggestive of malignant potential. Seven cases of cancer of the gland have been found, all in females, 2 in the younger age group (see Table 3). These tumors were relatively well differentiated, 3 papillary, 1 follicular, and 3 mixed types. Two were 2-3 cm, 3 about 1 cm and 2 between .5 and 1 cm in size and all were the tumor of concern on palpation. Four had localized metastasis or blood vessel invasion. The latent periods varied between 11 and 22 years. Most of the women in whom cancer was diagnosed had multiple pregnancies prior to development of their tumors. More than 5 years has elapsed in five cases without evidence \Y Thyroid Surgery was done by Drs. B.M. Dobyns, Case Western Reserve U, B. Colcock, Lahey Clinic and L.C. Mm PS tu ai} > Broadus, U.S. Navy. ;