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Long-term aspirin use reduces risk
for colorectal cancer
Higher doses needed to produce effect,
more research needed to clarify risks
BOSTON - August 23, 2005 - A new report from the Nurses'
Health Study finds that regular, long-term aspirin use can significantly
reduce the risk of colorectal cancer, as suggested by several earlier
studies. However, the benefit appears to require more than a decade
and is strongest at dose levels associated with a greater risk of
side effects such as bleeding. Similar results were found for non-steroidal
anti-inflammatory drugs (NSAIDS) such as ibuprofen and naproxen.
The report - from researchers at Massachusetts General Hospital
(MGH), Brigham and Women's Hospital and Dana-Farber Cancer Institute
- appears in the August 24 Journal of the American Medical Association.
"Several earlier studies have found that, among patients with
a history of colon polyps or cancer, regular aspirin treatment prevents
the recurrence of precancerous polyps. However, the ability of aspirin
to reduce the long-term incidence of invasive cancer has not been
well-demonstrated," says Andrew Chan, MD, MPH, of the MGH
Gastrointestinal Unit, the paper's lead author. "Our study
did find a protective effect of long-term aspirin use on risk of
invasive colorectal cancer, but only at dosage levels considerably
higher than those used to prevent cardiovascular disease."
The Nurses'
Health Study (NHS) has followed more than 120,000 female registered
nurses since the mid-1970s, asking them to complete a questionnaire
on risk factors for and incidence of cancer and cardiovascular disease
every two years. In 1980, assessments of diet and the use of aspirin
and NSAIDS were added. The current report analyzes information from
almost 83,000 NHS participants, among which 962 cases of colorectal
cancer were diagnosed during the 20-year study period.
While the incidence of colorectal cancer was lower in the women
who took aspirin regularly, the risk reduction was significant only
for those taking aspirin 10 years or longer. The benefit increased
as dosage levels rose, with the greatest risk reduction seen in
those taking more than 14 standard tablets per week. A similar risk
reduction was seen with the intake of NSAIDS, with greater benefit
also associated with higher dosage; but an analysis of acetaminophen,
which is believed to act through different mechanisms, found no
association of that medication with colorectal cancer. It is believed
that the ability of aspirin and NSAIDS to reduce cancer risk may,
at least in part, relate to their shared ability to inactivate the
COX-2 enzyme, which could stimulate tumor development.
The risk of serious gastrointestinal bleeding, a known side effect
of both aspirin and NSAIDS, also rose as dosage levels increased,
with bleeding occurring nearly twice as often in those taking the
highest doses. The researchers estimate that a high-dose aspirin
regimen that prevented one or two cases of colorectal cancer in
a population might also contribute to eight additional cases of
serious gastrointestinal bleeding.
"Before we can make any recommendations about whether patients
should take these medications to reduce their cancer risk, we're
going to need additional studies that clarify the risks and benefits
of such an approach, particularly compared to other prevention strategies.
For now, individuals need to discuss the options with their physicians"
says Chan, who is an instructor in Medicine at Harvard Medical School.
Chan and his colleagues have already initiated studies aimed to
further clarify the impact of long-term use of aspirin and NSAID
drugs, particularly in those at high risk for cancer and other chronic
diseases.
Additional authors of the study are Charles Fuchs, MD, MPH, senior
author, of Dana-Farber Cancer Institute and Brigham and Women's
Hospital (BWH); Edward Giovannucci, MD, ScD, Eva Schernhammer, MD,
DrPH, and Gary Curhan MD, ScD, all of BWH and the Channing Laboratory
at Harvard Medical School; and Jeffrey Meyerhardt, MD, MPH, of Dana-Farber.
The study was supported by grants from the National Cancer Institute,
the National Institutes of Health, the American Gastroenterological
Association and the Foundation for Digestive Health.
The Nurses' Health Study (NHS) was initiated in 1976 at BWH. The
NHS is the longest-running, major women's health study ever undertaken
and has resulted in hundreds of journal articles, many containing
groundbreaking findings on how to prevent some of the major causes
of disease and death in women.
Massachusetts General Hospital, established in 1811, is the original
and largest teaching hospital of Harvard Medical School. The MGH
conducts the largest hospital-based research program in the United
States, with an annual research budget of more than $450 million
and major research centers in AIDS, cardiovascular research, cancer,
cutaneous biology, medical imaging, neurodegenerative disorders,
transplantation biology and photomedicine. In 1994, MGH and Brigham
and Women's Hospital joined to form Partners HealthCare System,
an integrated health care delivery system comprising the two academic
medical centers, specialty and community hospitals, a network of
physician groups, and nonacute and home health services.
Media Contact: Sue
McGreevey, MGH Public Affairs
Physician Referral Service: 1-800-388-4644
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