A marked increase in the incidence of
papillary thyroid cancer in children has been documented in regions of the former Soviet Union most heavily contaminated by
radioactive fallout from the Chernobyl
nuclear power plant accident in April 1986. Accumulation of radioactive iodines by normal
iodine trapping mechanisms resulted in significant radiation doses to the thyroid gland. Although it has long been known that thyroidal radiation resulted in nuclear and
chromosomal abnormalities visible by light microscopy, modern molecular biology techniques are beginning to identify much smaller alterations in chromosomal coding sequences that are associated with malignant transformation. Although stable
chromosomal abnormalities can be detected in Chernobyl-associated
thyroid cancers, they are much less prevalent than in
thyroid cancers developing after external beam irradiation. However, several unique chromosomal breakpoints have been described in radiation-associated
thyroid cancers that are not commonly found in spontaneously occurring
thyroid cancer. Furthermore, activation of specific subtypes of the ret/PTC
tyrosine kinase oncogene appears to be more common in radiation-associated
thyroid cancers than in spontaneous
thyroid cancers. In summary,
thyroid cancers developing in the aftermath of the Chernobyl accident provide a unique opportunity to search for
chromosomal abnormalities that may be specific for radiation-induced
thyroid cancer.