Long-term aspirin use prevents some cancer.

Long-term aspirin use prevents some cancer

Once a simple headache reliever, aspirin now tantalizes physicians with its apparent ability to prevent strokes and heart attack. In addition, growing evidence suggests that aspirin also slashes the risk of getting cancer of the colon or rectum (SN: 3/16/91, p.166; 12/7/91, p.374).

Yet a 1993 study of more than 22,000 male physicians raised questions about aspirin's effectiveness against colorectal cancer. Investigators found that participants who took an aspirin tablet every other day for 6 years developed that cancer as often as those who took a placebo (SN: 8/7/93, p.85).

Now, in a report that may clarify the drug's cancer-fighting skill, investigators argue that aspirin does indeed dramatically lessen the risk of getting colorectal cancer--but only if it is consumed regularly for a decade or more.

"By taking aspirin, after 20 years, you cut your risk almost in half," says Edward Giovannucci of Brigham and Women's Hospital in Boston.

Giovannucci and his colleagues at Harvard Medical School and Harvard School of Public Health in Boston discuss their research in the Sept. 7 New England Journal of Medicine. In their analysis, they use the Nurses' Health Study, a biennial medical survey of female nurses begun in 1976.

The investigators divided the nurses into two groups: those who didn't take aspirin and those who consistently took two or more tablets every week. After documenting how many in each group got colorectal cancer over the years, Giovannucci and his colleagues calculated each group's cancer risk at various stages in the ongoing study.

The investigators found that nurses who took aspirin frequently for 20 years or more had a 44 percent lower risk of getting colorectal cancer than nurses who did not take aspirin. In contrast, those taking aspirin for 9 years or less enjoyed no discernible cancer protection.

Though the investigators report that women who consumed aspirin for 10 to 19 years lowered their risk of cancer by 30 percent, Giovannucci cautions that the study does not have enough statistical power to make that finding reliable.

"It does appear that duration of use is very important," says Peter H. Gann of Northwestern University Medical School in Chicago, an epidemiologist who participated in the 1993 study.

Among the nurses taking aspirin for 20 years or more, those taking at least four to six tablets a week experienced the greatest reduction in colorectal cancer risk. Comparable doses appear to help the cardiovascular system, Giovannucci notes.

In a commentary accompanying the report, physician Aaron J. Marcus of New York Veterans Affairs Medical Center in New York City argues that there is now enough evidence of aspirin's cancer- fighting talent to warrant prescribing it for people at high risk of colorectal cancer.

But Marcus and other researchers still hesitate to suggest that the general population start popping an aspirin tablet every other day. Long-term low-dose aspirin therapy may have disadvantages that for some people outweigh the benefits, they note. For instance, Marcus says, "aspirin may cause unnecessary bleeding."

As investigators grow more confident in their belief that aspirin can prevent colorectal cancer, their research will focus more on how the drug achieves its surprising effect. "We have to find out why it takes so long to work," says Marcus.