Validity of thyroid cancer incidence data following the Chernobyl accident.

The only clearly demonstrated cancer incidence increase that can be attributed to radiation from the Chernobyl accident is thyroid carcinoma in patients exposed during childhood or adolescence. Significant increases in thyroid disease were observed as soon as 4 y after the accident. The solid/follicular subtype of papillary carcinoma predominated in the early period after the accident. Morphological diagnosis of cancer in such cases, if no infiltrative growth is clearly visible, depends mainly on the nuclear criteria. Outdated equipment and insufficient quality of histological specimens impeded reliable evaluation of the nuclear criteria. Access to foreign professional literature has always been limited in the former Soviet Union. The great number of advanced tumors observed shortly after the accident can be explained by the screening effect (detection of previously neglected cancers) and by the fact that many patients were brought from non-contaminated areas and registered as Chernobyl victims. It is also worth noting that exaggeration of the Chernobyl cancer statistics facilitated the writing of dissertations, financing of research, and assistance from outside the former Soviet Union. "Chernobyl hysteria" impeded nuclear energy production in some countries, thus contributing to higher prices for fossil fuel. The concluding point is that since post-Chernobyl cancers tend on average to be in a later stage of tumor progression, some published data on molecular or immunohistochemical characteristics of Chernobyl-related cancers require reevaluation.