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TMI Cancer Study: Radiation, Health and Questionable Claims

Researchers at the Penn State College of Medicine recently published a study claiming that analysis of thyroid tumors showed tissue differences, based on where the patient lived. People who lived near Three Mile Island at the time of the 1979 accident had tumors more likely to have come from radiation exposure than people who developed thyroid cancer while living elsewhere, according to the researchers.

Science is advanced by experts who publish new findings, and readers who then evaluate the conclusions and how they fit into the existing body of knowledge. We welcome all contributions to knowledge. But scientific studies should be read with care, so their claims can be understood, and so we can determine how the findings fit with what was previously understood. And these findings don’t fit.

Three Mile Island
Three Mile Island Nuclear Generating Station

Despite what a reader might assume from a news headline, this paper does not assert that Three Mile Island is the cause of any cancers. It goes off in a new direction, in ways that may not be obvious to a reader unfamiliar with previous work in the area.

The scientific consensus is that examination of a tumor, and its DNA, does not conclusively tell you what caused the tumor to develop. The other is that extensive work, in scientific and engineering disciplines far distant from medical science, has concluded the amount of radioactive material released from the reactor building during the Three Mile Island accident in March, 1979, was very small, and that doses to people in the region were minuscule, adding a tiny increment to the natural background exposure.

To be sure, the researchers made only limited claims. They did not say anything, for example, about whether that part of Pennsylvania saw any increase in thyroid cases. (Other studies show that it didn’t.)

They wisely pointed to some shortcomings of their study: Small sample size, and among the sample tumor material that they could gather, the inability to definitively analyze the genetics of some of the material. There were only 15 people in what they called the “at risk” group. They couched their conclusions with conditional terms like “may” and “likely,” but called for more study.

But one basic problem is that you cannot look at a tissue sample and say that radiation was the cause of the tumor. The human thyroid is potentially vulnerable because the thyroid naturally concentrates iodine that is present in the environment, and reactors create a form of iodine that is radioactive. There are some publications suggesting that some of the genetic mutations that are discernible in tumors are more prevalent in people who have been exposed to very large amounts of radioactive iodine. But this is not generally accepted as definite.

Plus, experience has shown that radioactive iodine is only likely to cause cancer in one category of people: children. Even among A-Bomb survivors, the group that had excess thyroid tumors was 21 and under. Tumors in this study were taken from people in the Three Mile Island area with an average age of 28.

There is another problem with the sample, in addition to its small size. All the patients in the sample were treated in only one facility, in Hershey. There are many other facilities which would treat thyroid cancer. And people living in the area did not always stay there; they would leave the area (to go to college etc.). So the “at risk” population is not well defined.

Perhaps most important of all, the maximum possible doses in the Three Mile Island area were approximately 1,000 times smaller than those we believe can cause cancer, because releases of iodine were very small. The Penn State researchers did not make any statement about the level of dose.

The above is a guest post from Jerry Hiatt, senior project manager of radiation and materials safety at NEI.


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