Editorial: Radiation and thyroid cancer

Published in The Hindu on June 13, 2011

The frequency of papillary thyroid carcinoma occurrence in young people is about 1.5 per million a year. But following the 1986 Chernobyl calamity a sudden 100-fold increase was seen in its occurrence in Ukraine, Belarus, and Russia. In all, nearly 6,000 people developed thyroid cancer; about 4,000 of them had been children or adolescents at the time of the accident. But how does one distinguish naturally occurring thyroid cancer from that caused by radiation? A paper published recently in the Proceedings of the National Academy of Sciences provides the answer. Radiation-specific signature in a particular region of chromosome 7 was found in people who were exposed to radioactive Iodine-131 due to the Chernobyl accident. Changes in the number or structure of chromosome 7 were found to be associated with human cancers. While five genes have been identified as tumour-associated candidates, over-expression of one gene serves as a signature of radiation-induced tumour. While none of the patients from the control groups showed any change in the specific region on chromosome 7, 39 per cent of those exposed to radiation carried the signature. The study, which used samples obtained from the Chernobyl Tissue Bank, covered a cohort of 52 radiation-exposed patients and a validation cohort of 28 radiation-exposed patients. The age-matched control groups had no exposure to radiation. Since only a subgroup of those exposed to radiation carried the signature, the scientists postulate the existence of other typical genetic markers.

Unlike other cancers, radiation-induced papillary thyroid carcinoma is easily preventable. Radioisotope Iodine-131, which has a half-life of eight days and the same physical properties as stable iodine, competes with it, and the thyroid gland has no way of telling them apart. Saturating the gland with stable iodine drugs taken as a prophylactic and avoiding the consumption of milk can prevent Iodine-131 from entering the gland. Such preventive steps are extremely important in the case of children. These measures, which were unfortunately not taken after the Chernobyl accident, have been adopted post-Fukushima. The new study should serve as a warning to people running nuclear plants that in the light of what we now know about radiation exposure and thyroid cancer, any delay in taking preventive steps will be extremely costly in terms of human lives and well-being.