News: A Vaccine for Colon Cancer.
- From: Ye Old One <usenet@xxxxxxxxx>
- Date: Tue, 28 Jul 2009 22:27:27 GMT
A Vaccine for Colon Cancer
A new approach to preventing cancer teaches the immune system to seek
and destroy emerging tumors.
By Jocelyn Rice
A cancer vaccine with a twist is making headway in clinical trials at
the University of Pittsburgh School of Medicine. Rather than targeting
a cancer-related virus--the way Gardasil targets human papillomavirus
to prevent some cervical cancers--the new vaccine triggers the immune
system to attack a faulty protein that's often abundant in colorectal
cancer tissue and precancerous tissue.
The Pitt investigators say that if the vaccine is successful, it could
potentially obviate the need for repeated colonoscopies in patients at
high risk for developing colorectal cancer. These patients have had
multiple precancerous polyps, called advanced adenomas, in their
intestines, and they are routinely screened by colonoscopy for signs
The vaccine has already proven safe in patients with advanced
pancreatic cancer. It is now in clinical trials to gauge the immune
response it elicits in patients with a history of advanced adenomas.
It works by spurring the body to manufacture antibodies against the
abnormal version of a mucous protein called MUC1. While moderate
amounts of the protein are found in the lining of normal intestines,
high levels of a defective form of MUC1 are present in about half of
advanced adenomas and the majority of colorectal cancers.
The vaccine primes the immune system to monitor the gut for emerging
cancers by teaching it to recognize abnormal MUC1. If an adenoma
develops and begins to produce the faulty version of MUC1, the immune
system will raise antibodies to attack and destroy the precancerous
"You would be using your immune system as a surveillance mechanism to
prevent the development of malignancy," says principal investigator
Robert E. Schoen, professor of medicine at the University of
Pittsburgh School of Medicine and professor of epidemiology at Pitt's
Graduate School of Public Health.
Using this kind of immunotherapy to combat cancer isn't new--a number
of cancer vaccines are currently being tested in clinical trials. But
so far the technique has been used only to attack existing tumors. The
new vaccine represents the first attempt to use immunotherapy to keep
cancer from forming in the first place. "This is taking it in a
different direction," says Schoen. "We're now trying to use
immunotherapy as a means of prevention."
Not all colorectal tumors produce abnormal MUC1, and there's no way to
know ahead of time if a patient will develop one that does. So it's
still theoretically possible to develop colorectal cancer even if the
vaccine is effective, says Schoen, because a vaccinated patient would
still be at risk for tumors that don't make faulty MUC1.
For that reason, it's not clear yet whether the vaccine could supplant
colonoscopies altogether in high-risk patients, says Mack Ruffin IV,
professor of family medicine and a research scientist in epidemiology
at the University of Michigan, who is not involved in the trials. "If
they still need colonoscopies, we haven't done anything but add extra
cost and side effects to managing people with polyps."
The Pitt investigators have been recruiting subjects for the trial
since October 2008, and they expect to finish gathering data in fall
2011. Patients receive an initial dose of the vaccine with boosters 2
and 10 weeks later, and their immune response is monitored for a year.
Because their history of advanced adenomas puts them at high risk for
cancer, the patients are monitored throughout the trial with
colonoscopies--the current gold standard for surveillance--giving the
researchers a preliminary idea of whether the vaccine can limit
recurrence or progression.
So far, in the more than 20 subjects already enrolled, says Schoen,
"the vaccine is extremely well tolerated." Beyond some redness and
soreness at the injection site and the occasional short-term fever,
there have been no adverse effects. The next step, Schoen says, will
be another trial to determine more precisely the relationship between
vaccine administration and adenoma recurrence. He estimates that those
experiments could begin within two years.
Abnormal MUC1 isn't limited to colorectal cancer. It's also present in
some other cancers, including most breast tumors, meaning the new
vaccine could be adapted for other uses. More broadly, the strategy of
stimulating the immune system to attack a tumor-related protein may be
relevant for other types of cancer as well. Many proteins are known to
be aberrantly expressed in malignant tissue, says Schoen, and
"vaccines against other proteins could be used for other cancers."
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