Cytogenetic changes in radiation-induced tumors of the thyroid

Thyroid carcinoma incidence is increased significantly after ionizing irrad iation; however, the possible mechanisms have not yet been identified. To p rovide clues for an understanding of the radiation-induced transformation o f thyroid epithelium, we analyzed the karyotypes of 56 childhood thyroid tu mors that appeared in Belarus after the Chernobyl nuclear accident in 1986, We also studied eight secondary thyroid tumors that developed after radiot herapy. Metaphase preparations obtained from primary cultures were analyzed by G-banding, Clonal structural aberrations were found in 13 of 56 Belarus sian cases and in 6 of 8 secondary tumors that developed after radiotherapy . Furthermore, we detected multiple chromosomal aberrations as well as comp lex rearrangements in some of these tumors and performed a detailed analysi s of marker chromosomes from a single case using spectral karyotyping and c omparative genomic hybridization in a childhood tumor from Belarus with a n ear-triploid karyotype, Both comparative genomic hybridization and spectral karyotyping analysis revealed structural alterations affecting identical c hromosomes 1, 2, 9, and 13, among others. In addition to the known hot spot s of alterations in papillary thyroid carcinomas on chromosomes Iq and 10q, a comprehensive breakpoint analysis in the pooled data set revealed novel breakpoints on chromosomes 4q, 5q, 6p, 12q, 13q, and 14q, The chromosomal a berrations in these tumors may provide suitable starting points for the pos itional cloning of genes involved in radiation-induced tumorigenesis.