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New Finding May Hold Key to Understanding the Role of Radiation in Thyroid Cancer
Specific Genetic Defect Identified in Chernobyl Cancers
October 16, 1997 (Colorado Springs, CO) - A tell-tale genetic defect that has been identified in the thyroid cancers of children exposed to radiation from the Chernobyl disaster may lead to a better understanding of the precise role of radiation in the type and incidence of the disease in the United States, according to researchers at the American Thyroid Association (ATA) meeting.
There has been a dramatic increase in the rate of thyroid cancer in children from areas exposed to radiation after the Chernobyl nuclear power plant accident in 1986. In the Republic of Belarus as a whole, the rate of thyroid cancer has risen 40-fold, while in the immediate region most heavily contaminated by Chernobyl, the incidence has increased more than 100-fold.
"We have now found what appears to be a genetic signature for these Chernobyl-induced cancers," said Dr. James A. Fagin, of the Division of Endocrinology at the University of Cincinnati College of Medicine. In comparing the DNA of tumor specimens from 38 Chernobyl patients and from 17 patients in the Cincinnati and Los Angeles area who have had no known exposure to radiation, Dr. FaginÃs group identified a genetic defect in the ret oncogene (a gene associated with thyroid cancer) that occurred at more than three times higher frequency in the Chernobyl specimens.
In Dr. FaginÃs study, the Chernobyl patients had a much higher percentage of tumors with the ret oncogene mutation known as "ret/PTC3." The Chernobyl groupÃs incidence of ret/PTC3 tumors was 58 percent, compared to only 18 percent in the U.S. cases studied. This difference may help to explain why the Chernobyl tumors are more likely to be of the rarer and possibly more aggressive "solid variant type" of thyroid cancer, said Dr. Fagin.
Detecting Tumors Caused by Radiation Researchers have long known that a major risk factor for thyroid cancer is exposure to radiation in childhood, such as from once common x-ray treatments for enlarged tonsils, acne and ringworm of the scalp. According to Dr. Fagin, this type of study may eventually help researchers determine, "whether a tumor was induced by radiation by looking at a tumorÃs genetic signature," without prior knowledge of a patientÃs exposure to radiation. However, at the present time, tools to make that determination with absolute certainty do not exist. Further research is also needed to determine whether the ret/PTC3 abnormality appears in patients exposed to other forms of radiation.
Each year, about 15,600 Americans are diagnosed with thyroid cancer, with women three times more likely than men to develop the disease. The first and only sign of thyroid cancer is often an enlarged thyroid gland or a nodule (bump) on the thyroid gland, but only 10 percent of detected thyroid nodules, are malignant. Of those diagnosed with the disease, survival rates are high with proper treatment - an estimated 500,000 Americans are alive who have had thyroid cancer.
The American Thyroid Association (ATA) is a professional society of more than 700 members dedicated to research and treatment of thyroid pathophysiology. One thousand physicians and scientists are attending the 70th annual meeting of the ATA in Colorado Springs, Colorado, October 15-19, 1997.
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