Can Aspirin Prevent Cancer?

HEALTHBEAT: Can Aspirin Prevent Cancer? Jury's Still Out After New Studies

The research could give you whiplash: Aspirin prevents cancer, one study
says. Oops, maybe not, says another. Now comes word that aspirin may
fend off cancer only if people take much more than is used to fight heart
disease, suggesting some of the earlier back-and-forth may have been
due to confusion over the right dose.

Monday, April 23, 2007 1427 PDT


WASHINGTON, D.C. -- The research could give you whiplash: Aspirin
prevents cancer, one study says. Oops, maybe not, says another. Now
comes word that aspirin may fend off cancer only if people take much more
than is used to fight heart disease, suggesting some of the earlier
back-and-
forth may have been due to confusion over the right dose.

Even that evidence is circumstantial, offering no end to the competing
headlines.

"A general perspective that people have is, 'Why is it so difficult to get a
clear answer on a pill that costs a few pennies and is available
over-the-counter and taken by millions of people?'" says the American
Cancer Society's Dr. Michael Thun, a coauthor of the newest study.

For decades, scientists have chased the hope that aspirin could be an easy
way to prevent certain cancers. The idea: Aspirin fights inflammation, and
thus pain, by inhibiting substances known as cyclooxygenase, or COX,
enzymes. COX enzymes also are involved in the formation of certain kinds
of tumors, such as colorectal, prostate and breast cancers.

Aspirin does something else, as well: It makes blood less likely to form
clots, giving it an important role in fighting heart disease. A daily baby
aspirin _ 81 milligrams _ is recommended for people with cardiovascular
disease or who are at high risk for it.

In contrast, connecting the cancer dots _ showing that reducing COX would
in turn reduce tumors _ is vexing. And because aspirin can cause stomach
ulcers and bleeding, firm proof of an anticancer benefit is a must before
any
health group will recommend using it for that reason.

The hints of that benefit are tantalizing.

"Aspirin and cancer's not going to go away, and there's great value in
figuring out how to use it," says Dr. Phillip Febbo, an oncologist at Duke
University Medical Center who is closely following the research.

Aspirin and similar anti-inflammatory drugs reduce the risk of many cancers
when tested in animals bred to develop human-like tumors. Evidence in
people isn't nearly so clear-cut.

In so-called observational studies, people who say they regularly use
aspirin seem at lower risk of colorectal cancer in particular, and also
prostate, breast and a few other cancers. However, people who take
aspirin on their own may be healthier than the general population and
thus at lower risk of cancer anyway.

Some more rigorous trials randomly assigned people at high risk of colon
cancer to use aspirin, and found those who did developed fewer precancerous
growths called polyps _ but stopped short of showing the drug really
prevented cancer, Thun explains. More disappointing news came in 2005,
when a major study that assigned women to use either a baby aspirin or
dummy pills found no effect on a whole list of cancers.

Thun and colleagues at the cancer society wondered if many of those earlier
studies used too low a dose of aspirin to have an anticancer effect. So they
examined adult-strength aspirin _ 325 mg or more _ in a study tracking more
than 140,000 people.

Taking an adult-strength aspirin daily for at least five years was
associated with a 30 percent lower risk of colorectal cancer, a 20 percent
lower risk of prostate cancer, and 15 percent less cancer overall, they
reported last week in the Journal of the National Cancer Institute.

That's not proof of aspirin's benefit, either, but it does suggest that
clinical trials start looking at higher doses to tease out an answer.

Duke's Febbo says answers also may come from improved testing of the
COX enzyme's role in individual tumors. As with other tumor stimulators,
there may be subsets of people for whom COX is a big cancer factor,
and others where COX, and thus aspirin, won't matter.

Until then, what's the average person to do? Neither the cancer society nor
a government committee that sets health guidelines recommends aspirin to
prevent cancer, even for those at high risk of colorectal cancer. Consult a
doctor first if you're considering it anyway, Thun stresses -- aspirin can
be dangerous if someone bleeds easily or has certain other conditions.

For now, cancer specialists quote their cardiac colleagues' advice.

"Stick with what's heart-healthy," says Febbo. And stay tuned: "There's
a lot of potential for aspirin and cancer."


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