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Ongoing observational follow-up of participants in the Women’s Health Study suggests that long-term use of alternate-day, low-dose aspirin may reduce risk for colorectal cancer in healthy women.
The Women’s Health Study was a randomized, factorial trial of aspirin (100 mg every other day) and vitamin E in the primary prevention of cancer and cardiovascular disease with a median 10-year follow-up. The primary cancer end point was any invasive cancer (excluding nonmelanoma skin cancer); incidences of breast, colorectal, and lung cancer were secondary end points. The active intervention period ended in March 2004; participants were invited for further annual follow-up and offered the opportunity to opt out during 2005 and 2006.
Of the 39,876 female health professionals 45 years of age or older who enrolled in the study, 33,682 (88.6% of survivors) agreed to continue participation. There were 5,071 confirmed cancer cases (2,070 cases of breast cancer, 451 cases of colorectal cancer, and 431 cases of lung cancer) and 1,391 confirmed cancer deaths during the 18-year follow-up (through March 2012). There was no association between aspirin use and total cancer, breast cancer, or lung cancer; however, the risk of colorectal cancer was reduced in the aspirin group (HR, 0.80; 95% CI, 0.67–0.97]; P = 0.021), primarily for proximal colon cancer (HR, 0.73; 95% CI, 0.55–0.95; P = 0.022). Survival curves suggested that the difference emerged after 10 years, with a post-trial reduction of 42% (HR, 0.58; 95% CI, 0.42–0.80; P < 0.001).
Ann Intern Med. 2013;159(2):77-85 .