A team of researchers has found a link between the 1979 Three Mile Island nuclear accident and thyroid cancer cases in south-central Pennsylvania.
Three Mile Island (TMI), located near Harrisburg, Pennsylvania, had a partial meltdown accident on March 28, 1979. During the accident, radiation was released into the environment, which the United States Nuclear Regulatory Commission said was in small amounts with no detectable health effects.
Looking at tumour samples from people verified to have lived in the areas around TMI at the time of the accident, remained in the area and subsequently developed thyroid cancer, Penn State College of Medicine researchers observed a shift in cases to cancer mutations consistent with radiation exposure, from those consistent with random causes.
In this retrospective cohort study, meaning the patients in the study already had thyroid cancer and were known to have been exposed to the TMI accident, lead researcher David Goldenberg and colleagues identified 44 patients who were treated at the Penn State Milton S. Hershey Medical Center for the most common type of thyroid cancer - papillary thyroid cancer - between 1974 and 2014. The patients were then divided into two groups: at-risk and control groups.
Patients in the at-risk group were those who developed cancer between 1984 and 1996, consistent with known latency periods of radiation-induced thyroid cancer, and who lived in at-risk geographical areas, based on reported weather patterns, at the time of the accident.
"This definition was designed to allow us to identify relatively acute effects of radiation exposure from the accident," said Goldenberg.
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Patients who developed cancer outside of the expected latency period were placed in the control group.
While most thyroid cancers are sporadic, meaning they happen without clear reasons, exposure to radiation has been shown to change the molecular makeup of the cancer, according to the researchers.
The team observed an increase in the genetic mutation caused by exposure to low-dose radiation in the at-risk group and a decrease in the incidence of sporadic thyroid cancer, identified by a specific genetic mutation known as BRAF. The BRAF mutation is typically not present in the radiation-induced types of thyroid cancer.
The study indicated that these observations are consistent with other radiation-exposed populations.
In the control group, 83 percent of patients had the BRAF mutation. The BRAF mutation was found in only 53 percent of patients in the at-risk group. In the at-risk group, there was also a rise in other molecular markers seen in radiation-induced thyroid cancer, the researchers added.
"While no single marker can determine whether an individual tumour is radiation-induced, these data support the possibility that radiation released from TMI altered the molecular profile of thyroid cancers in the population surrounding the plant," Goldenberg said.
A limitation of this study is the small sample size, limited to tumour samples from patients treated for thyroid cancer at Penn State Health Milton S. Hershey Medical Center. The next step in the research is a study with a larger number of patients from other regional hospitals to determine if the correlation continues in a larger sample.
The study appears in the journal Laryngoscope.