Recent evidence suggests that daily aspirin use decreases cancer risk, particularly for colorectal cancer, but evidence for alternate-day use is scant.
Dr Nancy Cook and colleagues examined the association between long-term, alternate-day, low-dose aspirin and cancer in healthy women.
The research team performed an observational follow-up of a randomized trial in female health professionals.
The team evaluated 39,876 women aged 45 years or older in the Women's Health Study, 33,682 of whom continued observational follow-up.
The team assessed 100 mg of alternate-day aspirin or placebo through 2004, with a median 10-year follow-up.
Posttrial follow-up continued through 2012.
The researchers measured cancer incidence.
A total of 5071 cancer cases, and 1391 cancer deaths were confirmed.
Over the entire follow-up, aspirin had no association with total, breast, or lung cancer.
Colorectal cancer was reduced in the aspirin group, primarily for proximal colon cancer.
The team found that the difference emerged after 10 years, with a posttrial reduction of 42%.
There was no extended effect on cancer deaths or colorectal polyps.
More gastrointestinal bleeding and peptic ulcers occurred in the aspirin group.
Dr Cook's team commented, "Long-term use of alternate-day, low-dose aspirin may reduce risk for colorectal cancer in healthy women."