* Tumors can take 20 years to spread
* Problem will be finding effective screening method
* Early surgery can cure ailment
By Maggie Fox, Health and Science Editor
WASHINGTON (Reuters) - Pancreatic cancer grows
slowly, taking years and even decades to develop, a finding
that offers the chance to catch it early and cure it,
researchers reported Wednesday.
They said their findings confirm that one of the most
lethal cancers kills not because it spreads like wildfire, but
because it does not cause symptoms until it is advanced.
"That provides a large window of opportunity to try to
detect the presence of these cancers in the first 20 years of
their existence, before they become lethal," said Dr. Bert
Vogelstein of Johns Hopkins University in Baltimore, who helped
lead the study.
"If one can do that, one can in principle cure them by
surgery," Vogelstein added in a telephone interview.
Pancreatic cancer is one of the deadliest cancers, killing
95 percent or more of its victims within five years of
diagnosis. The American Cancer Society says 42,000 Americans
were diagnosed with pancreatic cancer in 2009 and more than
35,000 died of it.
Vogelstein's team, working with British researchers at the
Wellcome Trust Sanger Institute and the University of
Cambridge, did a kind of genetic archeological dig into
They collected tissue samples during autopsies immediately
after patients died from pancreatic cancer, as well as from
three patients whose tumors were surgically removed in an
attempt to save their lives.
In two papers in the journal Nature, they described how
they used mutations in the tumors as a "molecular clock" to
time the evolution of the tumors.
DNA mutates at a rate that can be calculated and the
researchers already knew which mutations were caused by
pancreatic cancer. They compared the DNA mutations in the
primary tumor -- the first tumor that grew in the pancreas --
to the secondary tumors in the liver and other organs.
CANCER FAMILY TREE
"We could kind of create a family tree with each successive
generation having additional mutations to the genes that
started the process," Vogelstein said.
"From doing that it was obvious that it took a very long
time, in fact decades, for the cancer to develop to its fully
malignant state. That means ... these cancers, at least most of
them, do not develop quickly but in fact more like other
cancers, including colon cancer."
They estimated it takes an average of 11.7 years before the
first true cancer cell develops within a precancerous lesion.
It takes another 6.8 years for a tumor to grow and the first
cancer cell to break off to go somewhere else in the body, and
then 2.7 years until the patient dies.
The hard part is going to be screening for pancreatic
cancer. Colon cancer can be found and prevented with
colonoscopies, which involve threading a camera through the
colon and removing pre-cancerous lesions when they are
But the pancreas is not easy to get to and even if a tumor
can be spotted before it gets too big, it requires complicated
surgery to get it out, Vogelstein said.
"The bowel you can just go in and snip it out, which is
great," he said.
His team is working on ways to find mutated DNA from
pancreatic tumors or pre-cancerous lesions in the blood. Other
teams are looking for ways to find circulating tumor cells,
while other groups may look at using MRI or CT scans to detect
the tumors before they cause symptoms.
(Editing by Eric Walsh)
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