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Genetic 'red flags' linked to colon cancer detection
New findings show a simple blood test
for genetic red flags could identify people at risk of colorectal cancer,
the second-leading cancer killer in the United States...
Researchers said this test might reduce the need for uncomfortable colon
and rectal exams.
"While much work still needs to be done before we can prove that this
is such a test, it would be exciting to be able to identify people at risk
of developing cancer before they get cancer," researcher Andrew
Feinberg, a geneticist at Johns Hopkins University in Baltimore, told
United Press International.
Colorectal cancer is expected to kill
more than 57,000 people in the United States in 2003, making it second
only to lung cancer when it comes to U.S. cancer-linked deaths.
While colorectal cancer develops with
few or no symptoms at first, colonoscopies and similar medical exams can
detect precancerous growths called polyps before they become
life-threatening.
"I've had a colonoscopy done, and
it's no fun, but everyone should do it," Feinberg said.
If colorectal cancer is found early,
some 90 percent of all patients survive.
Genetic defects
Earlier work by Feinberg and colleagues unearthed one of the first genetic
defects found to be involved in up to 40 percent of colon cancers.
Normally a person inherits two copies of
every gene, one from each parent. So-called "imprinting"
compounds usually stick to one of these copies and turn it off, leaving
the other copy on.
In cancer cases, imprinting patterns can
become abnormal, leading to the improper activation of a growth-promoting
gene called IGF2, or insulin-like growth factor II.
"When you have LOI (loss of
imprinting) of the IGF2 gene in colon cancer, the mother's gene copy gets
turned on by mistake and the cell gets a double dose of abnormal cell
growth," Feinberg explained.
Feinberg, along with geneticist Hengmi
Cui, gastroenterologist Marcia Cruz-Correa and colleagues, investigated
blood samples from 172 colonoscopy patients.
In findings reported in the journal Science,
they found the odds of finding specific LOI markers were five times
greater in patients with family histories of colorectal cancer. Patients
with a personal history of colorectal cancer were nearly 22 times more
likely to have these markers.
"We were very happy to find
this," Feinberg said. "There are no tests that identify risk of
cancer right now."
He cautioned this blood test still has
some five years to go before scientists can say for sure it predicts
colorectal cancer risk.
Studies needed
For one thing, long-term studies are
needed to confirm whether patients identified as high risk actually do –
or do not – go on to have increased colorectal cancer rates.
"We need to perfect the test, do
more experiments to make this test even more streamlined, easier to do,
cheaper. We need to extend these experiments to more patients and
different patient populations to validate these results," Feinberg
added.
Gastroenterologist C. Richard Boland at
Baylor University Medical Center in Dallas found the findings "very
interesting" and "worthy of a clinical trial, I should
think."
Clinical epidemiologist David Ransohoff
at the University of North Carolina in Chapel Hill added: "The
development of a non-invasive test for cancer has been the holy grail of
cancer detection research for three decades."
In the meantime, Feinberg urged everyone
at risk for colorectal cancer to undergo screening.
A Centers for Disease Control and
Prevention study finds that while more than a third of deaths from
colorectal cancer could be avoided if people aged 50 and older were
examined regularly, only about half of all U.S. men and women in that age
group had any type of screening.
The investigators also hope future
studies reveal therapies to correct the improper imprinting patterns to
fight cancer.
"It's easier to imagine coming up
with a drug that affects imprinting than to change a DNA mutation back to
normal," Feinberg said.
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