The finding contradicts standard textbook
assertions that radiation damage has no characteristic "signature."
It's important, the researchers believe, because it could provide a
clue to developing a treatment that protects specifically against
Led by UC's Yuri Nikiforov, MD, PhD, the
study was a collaboration between the pathology and internal medicine
departments and the Institute of Pathology at the University of Munich.
The team's findings are reported in the January edition of The Journal
of Clinical Investigation.
It is known that two types of genetic
damage appear in thyroid cancer cells--"point mutation," which affects
just one small sub-unit of the gene, and chromosomal "inversion," or
rearrangement, in which a piece of genetic material breaks off the
chromosome and reattaches itself in the wrong place.
What the research team now reports in The
Journal of Clinical Investigation is a type of chromosomal inversion
involving the BRAF gene that is characteristic of radiation-induced
thyroid cancer. By contrast, nonradiation, or "sporadic," thyroid
cancers are only associated with point mutations on that gene.
"This is a novel type of fusion in
thyroid cancer, and it's the first time that the BRAF gene has been
found to participate in chromosomal rearrangement," says Dr. Nikiforov.
"As a result of this finding," he says,
"we conclude that radiation in most cases is associated with specific
genetic damage--a chromosomal inversion.
"Finding that radiation exposure has its own mechanism is important," he says, "because it argues against the dogma.
"If we accept that radiation exposure
causes a specific type of DNA damage in the cells, we might be able in
the future to develop a pill or some other prophylaxis to prevent this
damage. That's our long-term goal."
Located in the throat below the larynx,
the thyroid gland secretes hormones vital to metabolism and growth. One
of few cancers that are increasing in recent years, although relatively
easily treated, thyroid cancer will be diagnosed in about 23,600
Americans in 2004, the American Cancer Society predicts.
Besides such factors as family history,
gender (women have a higher incidence) and age (the majority of cases
occur in people over 40), radiation exposure is one of the major causes
of thyroid cancer. The atomic bombs dropped on Hiroshima and Nagasaki
during World War II, and the melt-down at the Chernobyl nuclear power
plant in Ukraine, caused thousands of cases.
And before strict controls were imposed
in the 1960s on high-dose therapeutic radiation, then used routinely to
treat tonsils in children and thymus problems, medical exposure was
also a significant cause.
Currently the only protection for people
who risk potential radiation exposure, besides shielding from the
source, is prior doses of potassium iodide.