Cytokinesis-block micronucleus test in patients undergoing radioiodine therapy for differentiated thyroid carcinoma.

Cytokinesis-blocked micronucleus assay (MNT) was applied in the peripheral blood lymphocytes of patients undergoing radioiodine-131 ((131)I) therapy for differentiated thyroid carcinoma (DTC) after thyroidectomy to assess the genotoxic risk of this therapy. The amount of administered (131)I activity varied from 3,330 to 4,030 MBq. Blood samples were taken immediately before (131)I administration and one month later, along with routine blood tests. Twenty-six patients underwent radioiodine ablation (RIA) or radioiodine therapy (RIT) after radical thyroidectomy. The aim of this therapy was to ablate residual thyroid tissue, to treat lymph node metastases and/or distant lung metastases. The amount of orally administered activity of (131)I ranged between 3,330 and 4,030 MBq according to the kind of therapy (RIA or RIT). In five patients the cytogenetic analysis was performed immediately before and one month after the second therapy which was given to them 6 months to 1 year after the first. Three patients were male and 23 female. The age of the patients ranged between 23 and 76 years (mean age: 48.6 years). Results show that after radioiodine therapy there is a significant increase in the frequency of micronuclei. Comparing the average frequency of micronuclei in the patients studied before and after (131)I, a more than doubling increase was found. Mean values +/- SD of the patients before and after (131)I therapy were 10.72 per thousand +/- 5.84 per thousandand 25.28 per thousand +/- 12.6 per thousand respectively. These findings indicate a genotoxic activity of (131)I therapy estimated after a period of one month.