Persistence of micronuclei in peripheral blood lymphocytes of thyroid cancer patients 24 months after treatment with 131I

Complete text of publication follows. Objective: The persistence of DNA damage after exposure of human populations to low LET radiation is a key issue in radiobiology. The aim of this work is to present micronuclei data from a set of non-familial thyroid cancer patients that have undergone treatment with the same dose of 131I (2590 MBq; 70 mCi) following surgical thyroidectomy. We have previously shown that, up to six months after 131I treatment, a mild but significant and persistent increase in the frequency of micronucleated lymphocytes was observed in the 19 patients studied. The work reported here is a further step on the micronuclei analysis, by following the patients 24 months after the treatment in order to evaluate if the DNA damage was still present. Methods: The cytokinesis-blocked micronucleus (CBMN) assay was performed with whole blood cultures. The frequency of micronucleated binucleated lymphocytes (per mille MNBN) presented 24 months after therapy was compared with the levels observed before any therapy. The number of patients involved in the present study was 11, since 8 patients from initial group were submitted to an additional 131I treatment, and therefore excluded. Results and Conclusion: At 24 months after therapy the per mille MNBN (mean value ± SEM) increased from the pre-therapy value of 5.5 ± 1.3 to 9.6 ± 0.8 (P<0.05). This represents a near 2-fold increase of the initial levels of DNA damage presented by the patients. Furthermore, the increase herewith observed is similar to the ones observed at 1 and 6 months after treatment, reinforcing that the induction of micronuclei is a persistent effect of 131I treatment.