Alternate-day use of low-dose aspirin reduced the risk for colorectal cancer in women after 10 years, according to study results published in the Annals of Internal Medicine.
Researchers observed no reductions in risk for breast or lung cancers.
Prior studies suggest daily aspiring use reduces risk for certain cancers, particularly colorectal cancer, but there is limited evidence related to the effects of alternate-day aspirin use, according to background information in the study.
Nancy R. Cook
Nancy R. Cook, ScD, associate biostatistician at Brigham and Women’s Hospital and professor of medicine at Harvard Medical School, and colleagues conducted an observational analysis of 39,876 female health professionals enrolled in the Women’s Health Study.
The women were randomly assigned 100 mg of aspirin (n=19,934) or placebo (n=19,942) every other day from 1993 to 2004.
All participants were aged 45 years or older and had no prior incidence of cardiovascular disease or cancer aside from non-melanoma skin cancer.
The women completed yearly questionnaires through 2004 to document medication use and other health information. Invasive cancer incidence served as the primary endpoint. Breast, colorectal and lung cancer incidence served as secondary endpoints.
Median follow-up was 10.3 years.
At the time of the first post-trial questionnaire in 2005-06, researchers determined 1,875 (4.7%) of the women had died. The difference in death rate between the two groups — 4.8% for the aspirin group and 4.6% for the placebo group — was not statistically significant (P=.58).
After this point, 33,682 of the women agreed to continue extended follow-up (median, 17.5 years; range, 10.4-18.8 years).
After extended follow-up, researchers reported 5,071 cancer incidences among study participants. They included 2,070 breast cancers, 451 colorectal cancers and 431 lung cancers.
The researchers found no significant differences in the overall number of confirmed cancer cases between the aspirin and placebo groups (HR=0.97; 95% CI, 0.92-1.03).
Breast cancer and lung cancer incidence was comparable between the two groups (HR=0.98; 95% CI, 0.90-1.07).
However, researchers noted colorectal cancer incidence was lower in the aspirin group compared with the placebo group (HR=0.80; 95% CI, 0.67-0.97). The most significant reduction was in proximal colon cancer (HR=0.73; 95% CI, 0.55-0.95).
The difference in colon cancer incidence between the groups emerged after the 10-year active intervention period, with a post-trial reduction of 42% (HR=0.58; 95% CI, 0.41-0.81), researchers wrote.
“Aspirin’s adverse effects…cannot be forgotten,” the researchers concluded. “Whether new results about long-term benefits for cancer will tip the balance in favor or aspirin remains to be determined.”
Researchers reported no extended effect on colorectal polyps or cancer deaths.
Aspirin use was associated with increased incidence of gastrointestinal bleeding (HR=1.14; 95% CI, 1.06-1.22) and peptic ulcers (HR=1.17; 95% CI, 1.09-1.27). Three deaths due to gastrointestinal bleeding occurred in each study arm.
“The lack of a reduction in all-cause mortality, or even in the risk for all cancer, with aspirin in the Women’s Health Study should temper any recommendations for widespread use of aspirin in healthy middle-aged women,” Peter M. Rothwell, MD, PhD, of the University of Oxford wrote in an accompanying editorial.
“Benefits might be greater with daily aspirin, but any consequences for overall outcomes in women would probably be small given that the colon, esophagus and stomach together accounted for only about 8% of cancer cases in the Women’s Health Study, whereas they accounted for about 23% of all cancer deaths in men in the trials of daily aspirin,” Rothwell wrote. “The Women’s Health Study findings therefore reinforce the need to consider the risks and benefits of aspirin separately in men and women, and treatment decisions in individuals should now reflect what is known about their risk for gastrointestinal cancer as well as their vascular risk.”
Disclosure: See the study for a full list of the researchers’ relevant financial disclosures.