Chernobyl-related thyroid cancer: what evidence for role of short-lived iodines?

Over 500 cases of thyroid cancer were diagnosed in Belarus between 1986 and 1995 among persons exposed as children (under 15 years of age) to radioactive contamination from the Chernobyl nuclear accident. There is little doubt that radioactive iodine isotopes emitted during the nuclear explosion and subsequent fire were instrumental in causing malignancy in this particular organ. Comparison of the observed geographic distribution of Chernobyl-associated thyroid cancer incidence rates by districts with contamination maps of radioactive fallout shows a better fit for estimated 131I contamination than for 137Cs. Because 131I used for medical purposes had not been considered carcinogenic in humans in the past, and in view of the unusually short latency period between exposure and clinical manifestation of cancer, it is suspected that not only 131I but also energy-rich shorter-lived radioiodines may have played a role in post-Chernobyl thyroid carcinogenesis. Measurements of iodine isotopes are not available, but reconstruction of geographic distributions and estimations of radioactive fallout based on meteorological observations immediately following the accident could provide a basis for comparison with the distribution of thyroid cancer cases. In this paper, data from the Epidemiological Cancer Register for Belarus will be used to show geographic and time trends of thyroid cancer incidence rates in the period from 1986 to 1995 among persons who were exposed as children, and these will be compared with the estimated contamination by radioiodines. Tentative conclusions are drawn from the available evidence and further research requirements discussed.