Twenty years' experience with post-Chernobyl thyroid cancer.

Chernobyl, the largest ever nuclear accident, caused a huge release of radioactive isotopes, including nearly 2x10(18) Bq of iodine-131. Four years later an increase in thyroid cancer incidence, virtually all papillary carcinomas in children, occurred in the highly exposed areas. The increase has continued, and with increasing latency the tumour molecular and morphological pathology has changed; further changes may occur in the future. Children under the age of 1 at exposure show the highest susceptibility, and carry this risk with them into adult life; 4000 cases have been attributed to the accident, but so far very few have died. The risk falls rapidly with increasing age at exposure; it is doubtful if there is any risk for adults at exposure. Other factors linked to susceptibility to thyroid carcinogenesis after Chernobyl include dose, iodine deficiency, and genetic factors. Other consequences are briefly covered.