CANCER RISK FROM IN UTERO EXPOSURE TO CHERNOBYL FALLOUT IN UKRAINE

Abstract

Background and Aims: - Iodine-131 (I-131), the major component of Chernobyl fallout and an isotope readily absorbed by the thyroid gland, has been clearly linked to a subsequent increase in thyroid cancer among those exposed in early childhood. The embryo/fetus could also be vulnerable given the small size of the gland, the proliferative activity of fetal thyroid cells, and the high rate of radioiodine accumulation from the maternal circulation after 12 weeks gestation. We evaluated risk of thyroid cancer from in utero exposure to I-131 and also explored the incidence of non-thyroid cancers. Methods: We identified 2,582 mother-child pairs from the northern region of Ukraine in which the mother was pregnant at the time of the Chernobyl accident or the two months following when I-131 fallout was still present. Individual fetal thyroid I-131 doses were estimated from I-131 activity in the mother’s thyroid (mean dose=72 mGy; range 0-3,230 mGy). From 2003-2006, the in utero cohort was screened using an in-depth, standardized clinical examination. To evaluate incidence of other cancers, we linked the cohort to the Ukrainian National Cancer Registry (UNCR) for the period 1997 (the earliest year for which electronic records were available throughout the study area) and 2008, and estimated the standardized incidence ratio (SIR). Results:Seven cases of thyroid carcinoma and one case of Hurthle cell neoplasm were identified at the time of screening. The estimated excess odds ratio per Gray for thyroid carcinoma was markedly elevated (EOR/Gy=11.9) although not significantly so (P=0.12). Preliminary results of record linkage with the UNCR identified 6 cases of non-thyroid cancer, including 2 brain gliomas, 3 cases of Hodgkin disease, and 1 choriocarcinoma. The SIRs were 0.9 for males (95% confidence interval (CI): 0.11, 3.28) and 1.8 for females (95% CI: 0.49, 4.66). A subsequent linkage is currently underway. Conclusions : The data suggest that in utero exposure to I-131 in Ukraine may have increased the risk of thyroid carcinoma 20 years after the Chernobyl accident. Given the young age of the cohort, the results for cancer incidence at other sites are based on small numbers and should be interpreted cautiously.