Penn State College of Medicine researchers have shown, for the first time, a possible correlation between the partial meltdown of the Three Mile Island Nuclear Generating Station and thyroid cancers in the counties surrounding the plant.
Three Mile Island (TMI), located near Harrisburg, Pa., 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 tumor 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, 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 Dr. David Goldenberg, professor of surgery, and colleagues identified 44 patients who were treated at the Penn State Health 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.
The study appeared in a supplement to Laryngoscope.
Patients who developed cancer outside of the expected latency period were placed in the control group.
Researchers searched through all thyroid cancer tumor samples in the hospital's possession from the study period for patients who lived in at-risk regions Dauphin, York, eastern Cumberland, Lancaster and western Lebanon counties. They used genealogical software to verify that the patient was in an at-risk area during the accident, remained until cancer developed and was treated at the Medical Center. The tumor samples of those patients who were positively linked to the TMI accident area were then processed through the Penn State Institute for Personalized Medicine to determine genetic makeup of the cancer.
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 researchers 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 indicates 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.