Multicolour FISH detection of radioactive iodine-induced 17cen-p53 chromosomal breakage in buccal cells from therapeutically exposed patients

Simultaneous labelling of 17cen and the p53 locus by multicolour FISH was u sed to monitor radioactive iodine-induced structural and numerical chromoso me abnormalities in buccal cells from 29 hyperthyroidism and thyroid cancer patients sampled before and after therapeutic treatment. This novel method ology allowed the efficient detection of 17p deletions leading to p53 allel ic deletions, 17p gains and whole chromosome 17 numerical abnormalities in epithelial cells. Highly significant increases in the frequency of cells wi th (i) 17p abnormalities (1.8-fold; P < 0.001), including p53 monoallelic d eletions (2.1-fold; P < 0.001) and 17p gains (3.5-fold; P < 0.001); (ii) ch romosome 17 numerical abnormalities (2-fold; P < 0.001); and (iii) simultan eous 17p breakage and chromosome 17 numerical abnormalities (2.3-fold; P < 0.001), were observed after radioactive iodine treatment. As expected, the major contribution to these increases was detected in hyperthyroidism patie nts compared with thyroid cancer patients who suffered thyroidectomy before radioactive iodine exposure and, therefore, experienced a rapid eliminatio n of the radioisotope, Considering that both the genetic endpoints and the target tissue are extremely relevant in carcinogenesis, it is suggested tha t the observed genetic damage could contribute to the reported increase in cancer risk of people therapeutically or accidentally exposed to radioactiv e iodine.