RESUMO
BACKGROUND: The Chernobyl accident caused an unprecedented increase in papillary thyroid carcinoma (PTC) incidence with a surprisingly short latency and unusual morphology. We have investigated whether unexpected features of the PTC incidence after Chernobyl were radiation specific or influenced by iodine deficiency. METHODS: PTCs from children from Belarus, Ukraine, and the Russian Federation exposed to fallout from Chernobyl were compared with PTCs from children not exposed to radiation from the same countries, from England and Wales (E&W) and from Japan. The degree and type of differentiation, fibrosis, and invasion were quantified. RESULTS: There were no significant differences between PTCs from radiation-exposed children from Belarus, Ukraine, and the Russian Federation and PTCs from children from the same countries who were not exposed to radiation. Childhood PTCs from Japan were much more highly differentiated (p < 0.001), showed more papillary differentiation (p < 0.001) and were less invasive (p < 0.01) than "Chernobyl" tumors, while tumors from E&W generally showed intermediate levels of degree and type of differentiation and invasion. There was a marked difference between the sex ratios of children with PTCs who were radiation exposed and those who were not exposed (F:M exposed vs. unexposed 1.5:1 vs. 4.2:1; chi(2) = 7.90, p < or = 0.01005). CONCLUSIONS: The aggressiveness and morphological features of Chernobyl childhood PTCs are not associated with radiation exposure. The differences found between tumors from the Chernobyl area, E&W, and Japan could be influenced by many factors. We speculate that dietary iodine levels may have wide implications in radiation-induced thyroid carcinogenesis, and that iodine deficiency could increase incidence, reduce latency, and influence tumor morphology and aggressiveness.