Long-term data on the risk of colorectal cancer according to dose, duration, and consistency of aspirin therapy are limited.
The team conducted a prospective study of 47,363 male health professionals aged 40 to 75 years at enrollment in 1986.
Dr Andrew Chan and colleagues from Washington, USA collected data on aspirin use, other risk factors, and diagnoses of colorectal cancer.
|In men using more than 14 aspirin tablets per week, the risk was 0.30|
The team confirmed all reports of colorectal cancer through 2004 by review of medical records.
The researchers documented during 18 years of follow-up, 975 cases of colorectal cancer over 761,757 person-years.
After adjustment for risk factors, men who regularly used aspirin had a multivariate relative risk for colorectal cancer, compared with nonregular users.
The team found that significant risk reduction required at least 6 to 10 years of use, and was no longer evident within 4 years of discontinuing use.
The team noted that the benefit appeared related to increasing cumulative average dose.
Compared with men who denied any aspirin use, the multivariate relative risks for cancer were 0.94 for men who used 0.5 to 1.5 standard aspirin tablets per week.
For use of 2 to 5 aspirin tablets per week, the risk was 0.80, and for 6 to 14 aspirin tablets per week the risk was 0.72.
In men using more than 14 aspirin tablets per week, the risk was 0.30.
Dr Chans' team concluded, "Regular, long-term aspirin use reduces risk of colorectal cancer among men."
"However, the benefit of aspirin necessitates at least 6 years of consistent use, with maximal risk reduction at doses greater than 14 tablets per week."
"The potential hazards associated with long-term use of such doses should be carefully considered."