Aspirin Slashes Colon-cancer Death Rates
People who regularly take aspirin cut in half their risk of dying from colon cancer, according to the largest, most
definitive epidemiologic study to investigate this link. The finding suggests
a relatively inexpensive strategy for battling a scourge that currently claims the lives of about 50,000 Americans annually.
The new work also adds weight to the findings of a much smaller study reported earlier this year. Although that retrospective study of about 6,000 men and women did not address cancer-survival rates,
it did indicate that regular aspirin use may reduce the incidence of colon cancer (SN: 3/16/91, p.166).
Spurred by those findings, epidemiologist Michael J. Thun and his colleagues at the American Cancer Society in
Atlanta correlated aspirin use and colon-cancer deaths among the 662,424 men and women they had been tracking since 1982 as
part of the societys Cancer Prevention Study. Upon entering the study participants
had answered a questionnaire covering a range of behavioral, dietary and lifestyle factors, including frequency of aspirin
use during the past year.
The risk of dying from colon cancer decreased with increasing aspirin use, Thuns team reports in the Dec. 5 NEW ENGLAND JOURNAL OF MEDICINE. Colon-cancer death rates among the most
frequent users-those taking aspirin 16 times or more per month were 60 percent as high as that seen in the study's aspirin abstainers. And when the researchers controlled for risk factors such as diet, obesity and family history of colon
cancer, the risk dropped to 50 percent of the colon-cancer death rate of the aspirin abstainers.
Its an interesting finding, says epidemiologist John A. Baron of Dartmouth Medical School in Hanover, N.H. He notes, however, that the new study does not prove that aspirin itself helps prevent
colon cancer. For examp1e, he points out that side effects of frequent aspirin
use, such as Intestinal bleeding may have caused members of this subgroup to seek medical attention more frequently than other
volunteers thereby increasing the likelihood that any developing colon cancer would receive early diagnosis. And early diagnosis increases the chance that a person with colon cancer will survive.
A large, randomized trial in which some people take aspirin and others take placebo pills would provide firmer evidence
of aspirins protection against colon cancer. But such a gold-standard study
might be difficult to conduct, Baron says, because people who know about aspirins widely publicized heart benefits (SN: 7/27/91,
p.55) might balk at the prospect of receiving placebo pills instead.*
For now, Baron and Thun remain cautious about advocating regular aspirin use for cancer prevention,
since it can cause potentially dangerous side effects.** At the same time,
they note that aspirin may provide secondary anticancer benefits for people who already take it to manage arthritis pain
or to reduce the risk of heart disease.
Even if epidemiologists can demonstrate that aspirin fights colon cancer, there remains the question of how it
exerts this effect. Like other nonsteroidal anti-inflammatory drugs (NSAIDs),
aspirin inhibits the synthesis of compounds called prostaglandins, which spur body cells including colon cells to proliferate. Thun suggests that aspirin might prevent rampant cell division a key attribute of cancers by interfering
win prostaglandin production.
A number of laboratory studies have shown that aspirin and other types NSAIDs inhibit the growth of chemical induced
colon tumors in rats and mice. Other studies have shown that an NSAI called sulindac
can shrink large-bow polyps in people. Such polyps, though benign, can develop
into cancers, Thun notes. Taken together, the individual pieces of evidence provide
scientists wit compelling reasons to further explore the link between aspirin and colon cancer, Thun contends. KA. Fackelman, Science News, 1994, p. 374.***
* The contravening variable of early medical attention due to intestinal bleed would
can be weeded out if they looked not at survival rates but rates of getting colon cancer. Early detection has little
impact in a long-term study.
** This problem as well as the identification of the placebo are laid to rest with the use of enteric
(coated aspirin), for it digests in the intestines, which is alkaline. Since
aspirin is a weak acid, its acidity neutralized, and thus as is to be expected the enteric aspirin does not cause stomach
bleedingand there is little risk of intestinal bleeding.
*** Subsequent studies have confirmed this prophylactic result and the science behind it.