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Women’s Health Study
Low-Dose Aspirin Does Not Prevent Cancer in Older,
Healthy Women
Lung cancer citied as possible exception
July 6, 2005 - A major study that includes nearly
40,000 healthy women found no benefit on preventing cancer from taking
low-dose aspirin, according to an article in the July 6 issue of JAMA.
The authors did conclude that “a beneficial effect on lung cancer cannot
be ruled out.”
A growing body of literature has supported a
protective effect of aspirin and other nonsteroidal anti-inflammatory
drugs (NSAIDs) on the development of cancer, according to background
information in the first article. Observational epidemiological
investigations suggest a strong inverse association, with risk
reductions as high as 20 percent to 50 percent for various cancer sites.
In contrast with the observational evidence on cancer incidence, data
from randomized trials, which provide more definitive results due to
their ability to minimize bias and confounding, have been far more
limited.
The Physicians’ Health Study (PHS) found no effect
on colorectal cancer of 325 mg aspirin administered every other day over
a 5-year randomized period or in post trial follow-up. In addition, no
randomized trial has yet assessed the impact of aspirin on the
development of breast cancer.
The Women’s Health Study (WHS) was a randomized,
double-blind, placebo-controlled trial, conducted between September 1992
and March 2004, evaluating the balance of benefits and risks of 100 mg
of aspirin every other day, and 600 IU of vitamin E every other day on
the primary prevention of cardiovascular disease and cancer in a cohort
of 39,876 healthy female health care professionals over an average
duration of 10.1 years.
Nancy R. Cook, Sc.D., of Brigham and Women’s
Hospital and Harvard Medical School, Boston, and colleagues evaluated
the findings for the aspirin component of the WHS with regard to cancer
risk. In this part of the study, 19,934 women received a dose of 100 mg
of aspirin every other day and 19,942 women received placebo.
The researchers found that aspirin had no observed
effect on total cancer, breast cancer, colorectal cancer, or cancer of
any other site, with the exception of lung cancer for which there was a
trend toward reduction in risk (22 percent reduced risk).
There was also no reduction in cancer death either
overall or by site, except for lung cancer death (30 percent reduced
risk). No evidence of differential effects of aspirin by follow-up time
or interaction with vitamin E was found.
“The findings from the WHS suggest that aspirin at
a dose of 100 mg every other day is not effective in reducing risk of
cancer in healthy women, although a beneficial effect on lung cancer
cannot be ruled out,” the authors wrote in conclusion.
“This large study of almost 40,000 women had a
duration of 10 years of treatment and follow-up, which was the longest
of any trial completed to date, and should be sufficient to detect
long-term effects. To determine whether higher doses of aspirin taken
daily would be effective in cancer prevention requires direct randomized
trial data. Such data would need to be considered in the context of risk
of gastrointestinal adverse effects before recommending higher-dose
aspirin for cancer chemoprevention among low-risk individuals,” the
authors conclude.
In an accompanying editorial, Eric J. Jacobs,
Ph.D., and Michael J. Thun, M.D., of the American Cancer Society,
Atlanta, commented on the findings.
“Should the null results with respect to cancer
from this large, well-conducted, long-term randomized trial, or from
other chemoprevention trials, be considered discouraging news for cancer
chemoprevention in general?
“There have been some successes in cancer
chemoprevention, such as the use of tamoxifen to prevent breast cancer
in high-risk women. However, currently, no agent has been shown to do
for cancer what statins do for cardiovascular disease, namely
substantially and relatively safely reduce disease occurrence in
individuals not at especially high risk.
“Pharmacological primary prevention of diseases as
heterogeneous as cancer is inherently difficult. Randomized trials of
cancer chemoprevention will undoubtedly produce many null results.
Nevertheless, continued systematic research on cancer chemoprevention,
including long-term randomized trials of carefully chosen agents, is
essential given the large potential benefits. At the same time, it is
unrealistic to expect the discovery of an agent that will produce
substantial reductions in overall cancer rates in the immediate future.”
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