Inverse association between age at the time of radiation exposure and extent of disease in cases of radiation-induced childhood thyroid carcinoma in Belarus

BACKGROUND, Increased incidence of childhood thyroid carcinoma, particularl y in the youngest children, has been reported from Belarus since the nuclea r reactor accident at Chernobyl in 1986. The relation between disease sever ity and age at the time of the accident, not previously established in this cohort, was analyzed in this study. METHODS. The authors studied the association between disease severity, expr essed by TNM classification, and age at radiation exposure in a cohort of 4 83 patients younger than 8 years at the time of the Chernobyl accident who have been diagnosed with differentiated thyroid carcinoma since 1986 at the Center for Thyroid Cancer in Minsk. The associations between age at radiat ion exposure and TNM categories were compared among ? groups of patients wh o were ages < 2, 2.1-4, 4.1-6, and 6.1-8 years at tine time of the accident . Multivariate discriminant analysis was performed to examine the effects o f age at the time of the accident, gender, histology, tumor stage, and N cl assification on the frequency of distant metastasis. RESULTS. Younger age at the time of the Chernobyl accident was associated w ith greater extrathyroidal tumor extension (P < 0.01) and more lymph node i nvolvement (P < 0.0001) and tended to be associated with more distant metas tases (P = 0.09). Compared with patients who were ages 6.1-8 years at the t ime of the accident, patients who were younger than 2 years had significant ly more extrathyroidal turner invasion (P = 0.004), lymph node involvement (P = 0.004), and distant metastases (P = 0.05). The age at diagnosis increa sed with older age at the lime of radiation exposure (linear regression ana lysis; correlation coefficient = 0.67; P < 0.001). Multivariate analysis re vealed that younger age at the time of the accident (P = 0.001) and advance d locoregional tumor extension (P < 0.001) were the only powerful factors i nfluencing the risk for distant metastasis of this malignancy. CONCLUSIONS. The severity of disease was associated inversely with age at t he time of radiation exposure in these cases of radiation-induced childhood thyroid carcinoma. Cancer 2000;88:1470-6, (C) 2000 American Cancer Society .