Possible
correlation shown between the partial meltdown at TMI and thyroid cancers
Penn State College of
Medicine
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.
"This definition
was designed to allow us to identify relatively acute effects of radiation
exposure from the accident," said Goldenberg.
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.
"While no single
marker can determine whether an individual tumor 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 tumor 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.
"All patients
were screened extensively to ensure that they lived in the vicinity of TMI from
the date of the accident until they developed thyroid cancer," Goldenberg
said.
"We used an extensive vetting process to ensure that patients
included in the study were present in at-risk counties at the time of the
accident and to confirm, to the greatest extent possible, that patients resided
in affected areas for their entire lives. Our study represents a static
population, which increased our ability to detect radiation-induced
cancers."
Past studies about
thyroid cancer and TMI have showed variable results, mainly because they were
demographic studies that looked at the entire population and not just those who
met the criteria of the current study.
"Much of the
variability associated with these studies is likely due to the relatively small
size of the population surrounding the TMI plant relative to the large
population required to detect statistically significant increases in cancer
incidence following low-level radiation, combined with a high degree of
mobility in the local population," Goldenberg said.