RAI Induces Genetic Damage

Cytogenetic damage after 131-iodine treatment for hyperthyroidism and thyroid cancer. A study using the micronucleus test.

Gutierrez S, Carbonell E, Galofre P, Creus A, Marcos R
Departament de Genetica i de Microbiologia, Universitat Autonoma de Barcelona, Bellaterra (Cerdanyola del Valles), Spain.

To detect the incidence and persistence of potential chromosome damage induced by iodine-131 therapy, we applied the cytokinesis-block micronucleus assay to peripheral blood lymphocytes from hyperthyroidism and thyroid cancer patients treated with 131I.

Two groups of patients were evaluated in a longitudinal study; one group was composed of 47 hyperthyroid patients and the other of 39 thyroid cancer patients.

In the hyperthyroidism group, the micronuclei frequency was determined before 131I therapy and 1 week, 1 month and 3 months after it.

Furthermore, an additional sample was taken from a subgroup of 17 hyperthyroidism patients 6 months after treatment.

In the thyroid cancer group, the analysis was also conducted over time, and four samples were studied: before treatment and 1 week, 6 months and 1 year later.

Simultaneously, a cross-sectional study was performed with 70 control subjects and 54 thyroid cancer patients who had received the last therapeutic dose 1-6 years before the present study.

In the hyperthyroidism group a significant increase in the micronuclei average was found over time.

In the sample obtained 6 months after therapy, the micronuclei mean frequency was practically the same as in the sample taken 3 months before.

In the thyroid cancer group a twofold increase in the frequency of micronuclei was seen 1 week after therapy.

Although this value decreased across time, the micronuclei frequency obtained 1 year after 131I therapy remained higher than the value found before it.

Concerning the data from the cross-sectional study, a significant increase in the frequency of micronuclei was detected in the subgroup of thyroid cancer patients treated between 1 and 3 years before the current study.

These results indicate that exposure to 131I therapy induces chromosome damage in peripheral lymphocytes and that the cytokinesis-block micronucleus assay is sensitive enough to detect the genetic damage by exposure to sufficiently high levels of radiation from internal radioactive sources.

Eur J Nucl Med 1999 Dec;26(12):1589-96
PMID: 10638411, UI: 20103766