Analysis of Short-Term and Stable DNA Damage in Patients with Differentiated Thyroid Cancer Treated with (131)I in Hypothyroidism or with Recombinant Human Thyroid-Stimulating Hormone for Remnant Ablation

It is well known that ionizing radiation can induce genetic damage and that oxidative stress is a major factor inducing it. Our aim was to investigate whether thyroid remnant ablation with low activities of (131)I (1,850 MBq) is associated with DNA damage by evaluating the CometAssay, micronuclei, and chromosome aberrations with multicolor fluorescent in situ hybridization. Methods: We studied 62 patients prepared with recombinant human thyroid-stimulating hormone (rhTSH) or by thyroid hormone withdrawal. In both groups, we analyzed stable and unstable genetic alterations before (131)I therapy and 1 wk and 3 mo after (131)I administration. We also correlated the genetic damage with several variables, including the degree of radiation-induced oxidative stress, genetic polymorphisms of enzymes involved in DNA repair, and antioxidative stress. Results: We found a comparable amount of DNA breaks evaluated by CometAssay and micronuclei testing in both groups of patients at different time points, but there was a significant increase in stable chromosome aberrations evaluated by multicolor fluorescent in situ hybridization (breaks and translocations) in patients prepared with thyroid hormone withdrawal. Overall, high chromosome damage was associated with higher retained body radioactivity and unfavorable gene polymorphism. A high level of free oxygen radicals and a low level of antioxidants were found in all patients at any time point. In particular, patients prepared with thyroid hormone withdrawal, at 3 mo, had significantly higher levels of free oxygen radicals than those prepared with rhTSH. Conclusion: An increase in stable chromosome aberrations with respect to baseline is detectable after administration of low doses of (131)I in patients prepared with thyroid hormone withdrawal but not in patients prepared with rhTSH. The clinical significance of these chromosomal alterations remains to be determined.