ASPIRIN USE AND COLORECTAL-CANCER - POSTTRIAL FOLLOW-UP DATA FROM THEPHYSICIANS HEALTH STUDY

Background: In contrast to most observational studies, the randomized Physicians' Health Study found no association between aspirin use and colorectal cancer after 5 years. Objective: To determine the effect of randomly assigned aspirin treatment and self-selected aspirin use on the incidence of colorectal cancer after 12 years and to identify fact ors influencing the self-selection of regular aspirin use. Design: Ran domized clinical trial and prospective cohort study. Setting: Male phy sicians throughout the United States. Patients: 22 071 healthy male ph ysicians who were 40 to 84 years of age in 1982. Intervention: 325 mg of aspirin every other day. In 1988, the aspirin arm of the randomized trial was stopped early. Participants then chose to receive either as pirin or placebo for the rest of the study. Measurements: Annual quest ionnaires asking about aspirin use and other variables, including occu rrence of cancer. Results: Colorectal cancer was diagnosed in 341 pati ents during the study period. Over 12 years of follow-up, random assig nment to aspirin was associated with a relative risk for colorectal ca ncer of 1.03 (95% CI, 0.83 to 1.28). Various gastrointestinal symptoms and diagnoses were strong predictors of less frequent aspirin use in 1988. The relative risk for colorectal cancer in persons who used aspi rin frequently after 1988 was 1.07 (CI, 0.75 to 1.53). Conclusions: In the Physicians' Health Study, both randomized and observational analy ses indicate that there is no association between the use of aspirin a nd the incidence of colorectal cancer. The low dose of aspirin used an d the short treatment period may account for the null findings. Howeve r, other characteristics associated with the use of aspirin in observa tional studies remain a plausible alternative explanation.