66 FALLOUT EFFECTS—MARSHALL ISLANDERS T goL Fe T 1 —tL BENIGN NODULES // 4 SOF f be f z } ra / / ye fy ‘ys ul a x DoTTa= “ae ye / a “ 5 a” 7 HYPOFUNCTION fs ‘ys a ‘/ 20 a yuY of od frowle oe 40 O 53 (600) (164) 4 CARCINOMA law TT ee Oe i 385 (53) 1 900 (16) “77-2, 1500 (6) EST. MEAN DOSE (rads) (No. in group) FIG. 1. Percent of persons with thyroid abnormalities (benign nodules, carcinomas, and hypo- function) in dose groups. All unoperated cases were considered benign for this calculation; therefore, the carcinoma incidence may be somewhat underestimated. Hypofunction includes both positive and suggestive cases. See text for composition of exposure groups. rads or more.* The 900-rad group represents the Rongelap children exposed at 2 to 9 years of age, the 385-rad group are Rongelap adults and Ailingnae children, and the 53-rad group are the Utirik people (adults and children). A few tentative interpretations might be drawn from the results in Fig. 1. Thyroid hypofunction appears to be a promoting factor for benign nodule development, since it roughly parallels the increase in nodularity at least in the 900-rad range. Perhaps such influence is reduced in the higher-dose group be- cause of the “overkill” effect. This interpretation would be in keeping with the high incidence of hypothyroidism, but with few thyroid tumors, following large doses of radiation for treatment of hyperthyroidism (17,18). A low correlation of carcinoma with hypofunction suggests that hypofunction plays less of a promoting role for malignant transformation or that a plateau is reached at certain doses for such transformation. A plateau effect and reduced incidence of cancer have been noted with other types of radiation-induced neoplasms in ‘It is noteworthy that of these six children five showed evidence of thyroid hypofunction with growth retardation, two of whom were myxedematous with markedly stunted growth but without thyroid nodules; four had thyroid nodules removed, of whom one has had a recurrence and another later died of acute myelogenous leukemia several years after thyroid surgery.