Thyroid consequences of the Chernobyl nuclear accident

It is well recognized that the use of external irradiation of the head and neck to treat patients with various non-thyroid disorders increases their r isk of developing papillary thyroid carcinoma years after radiation exposur e. An increased risk of thyroid cancer has also been reported in survivors of the atomic bombs in Japan, as well as in Marshall Island residents expos ed to radiation during the testing of hydrogen bombs. More recently, exposu re to radioactive fallout as a result of the Chernobyl nuclear reactor acci dent has clearly caused an enormous increase in the incidence of childhood thyroid carcinoma in Belarus, Ukraine, and, to a lesser extent, in the Russ ian Federation, starting in 1990. When clinical and epidemiological feature s of thyroid carcinomas diagnosed in Belarus after the Chernobyl accident a re compared with those of naturally occurring thyroid carcinomas in patient s of the same age group in Italy and France, it becomes apparent that the p ost-Chernobyl thyroid carcinomas were much less influenced by gender, virtu ally always papillary (solid and follicular variants), more aggressive at p resentation and more frequently associated with thyroid autoimmunity. Gene mutations involving the RET proto-oncogene, and less frequently TRK, have b een shown to be causative events specific for papillary cancer. RET activat ion was found in nearly 70% of the patients who developed papillary thyroid carcinomas following the Chernobyl accident. In addition to thyroid cancer , radiation-induced thyroid diseases include benign thyroid nodules, hypoth yroidism and autoimmune thyroiditis, with or without thyroid insufficiency, as observed in populations after environmental exposure to radioisotopes o f iodine and in the survivors of atomic bomb explosions. On this basis, the authors evaluated thyroid autoimmune phenomena in normal children exposed to radiation after the Chernobyl accident. The results demonstrated an incr eased prevalence of circulating thyroid antibodies not associated with sign ificant thyroid dysfunction. This finding is consistent with the short peri od of follow-up, but it is highly likely that these children will develop c linical thyroid autoimmune diseases in the future. Therefore, screening pro grammes for this at-risk population should focus, not only on the detection of thyroid nodules and cancer, but also on the development of thyroid auto immune diseases.