Aspirin may decrease risk of colon cancer.

Three years after the discovery that regular aspirin use can help prevent heart attacks - and barely a year after reports that it can lower the risk of strokes - new research hints that an aspirin a day helps keep colon cancer away.

The new epidemiologic study, involving more than 6,000 people, uncovered a statistical correlation between regular aspirin use and a reduced risk of colorectal cancer, the second leading cause of cancer deaths in the United States.

Earlier lab experiments had indicated that aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) inhibited the development of colon cancer in rodents. Inspired by those findings, Lynn Rosenberg of the Boston University School of Medicine and her colleagues decided to look for a similar connection in humans. Rodents serve as good models for the disease, she says, because they develop colon cancer in much the same way as humans.

Rosenberg's retrospective study focused on men and women treated in 16 East Coast hospitals between 1977 and 1988. At the time of admission, hospital nurses had administered questionnaires on past drug use to approximately 1,300 patients with colorectal cancer, 1,000 patients with other types of cancer and 4,000 patients with no personal history of cancer. In analyzing the questionnaires, the researchers accounted for known and suspected risk factors for colorectal cancer, including age, sex, family history, and alcohol and coffee consumption.

Men and women aged 30 to 69 who reported taking NSAIDs regularly - at least four times weekly for at least three months in the years preceding the study - appeared to have cut their risk of colorectal cancer in half, the team reports in the March 6 Journal of the National Cancer Institute.

Because almost all the frequently used NSAIDs contained aspirin, the researchers conclude that "the sustained use of aspirin-containing NSAIDs may inhibit the development of large-bowel cancer."

NSAIDs appeared to confer no colorectal benefit in people who had stopped taking the drugs regularly at least a year before the study - a finding that parallels experimental results with rats, the investigators note.

Although Rosenberg says the new data offer the first indication that aspirin may help inhibit colorectal cancer in humans, she cautions against drawing firm conclusions study" verifies the findings.

"This study fits in very well with our present understanding of colorectal cancer," comments Winfred F. Malone of the National Cancer Institute (NCI) in Bethesda, Md. Animal studies have yielded "very powerful results" on the ability of NSAIDs to inhibit prostaglandins, he says. These hormone-like compounds cause cells to grow rapidly, thereby increasing the chance that precancerous cells will develop into tumors. Moreover, Malone told Science News, preliminary, unpublished results of human trials at NCI suggest that the NSAIDs piroxicam, ibuprofen and sulindac redure the recurrence of precancerous polyps in the colon.

Malone says NCI researchers have not yet used aspirin in such trials because animal studies indicate that other NSAIDs have more powerful protaglandin-inhibiting effects. But the adds that Rosenberg's report should encourage cancer investigators to take a closer look at aspirin's apparent ability to reduce colorectal cancer risk.

If the epidemiologic findings survive further scrutiny, aspirin will join other substances known to affect colorectal-cancer risk. Diets high in fiber and calcium may reduce this cancer risk (SN: 8/4/90, p.69), while diets high in red meat may increase in risk (SN: 12/15/90, p.374).