THYROID LESIONS IN CHILDREN AND ADOLESCENTS AFTER THE CHERNOBYL DISASTER - IMPLICATIONS FOR THE STUDY OF RADIATION TUMORIGENESIS

Eight years after the Chernobyl nuclear accident, the most obvious eff ect is manifested by an increase in the prevalence of thyroid gland di seases in the exposed children and adolescents. In this study, we desc ribe a comparative analysis of epidemiological, clinical, and morpholo gical features of 92 malignant and 59 benign thyroid lesions from pati ents 5-18 yr of age exposed to radiation in Belarus as a result of the Chernobyl disaster. All of them were operated at the same institution during the period from September 1991 through December 1992. The high est number of patients that subsequently developed thyroid carcinomas was in the group that was less that 1 yr of age at the time of Chernob yl, and this number decreased progressively through age 12 yr. Convers ely, none of the patients with benign lesions only was less than 2 yr old at the time of the accident, and an exposure age of 5-6 yr was a t hreshold separating significant prevalence of malignant tumors in youn ger children from the more frequent benign lesions in older patients ( P < 0.001). Fifty-two percent of children with carcinomas and only 24% with benign lesions (P < 0.005) were residents of the Gomel region, w hich is the most contaminated in Belarus. The morphology of thyroid ti ssue adjacent to carcinomas showed a high prevalence of multinodular a nd diffuse changes, but not of adenomas or solitary adenomatoid nodule s. There was a high prevalence of focal micropapillary hyperplasia wit h graded degrees of severity, which we hypothesize may correspond to p recursors for papillary thyroid carcinoma in post-Chernobyl radiation- associated tumors.