However, the use of aspirin for chemoprevention of colorectal cancer may require using the drug at doses that are higher than recommended over a long period of time, which may cause serious side effects including gastrointestinal bleeding.

While the results of our study show that aspirin should not currently be recommended for the chemoprevention of colorectal cancer in a healthy population, there is a need for further studies to help identify for which patients the potential benefits outweigh the risks, according to Andrew T. Chan, MD, MPH, Massachusetts General Hospital and lead author of the study. We also need to improve our understanding of how aspirin works to prevent and inhibit the formation of colorectal cancer.

Study participants were enrolled in the Health Professionals Follow-up Study, a large prospective cohort study which has provided detailed and updated information on aspirin use.

Researchers found that men who used aspirin regularly experienced a significantly lower risk of colorectal cancer, including distal colon cancer, proximal colon cancer and rectal cancer, even after controlling for other risk factors. The reduction in risk was seen in both early (stage I/II) and advanced (stage III/IV) colorectal cancers. There were 975 documented cases of colorectal cancer over 761,757 person-years, among the 47,636 eligible men. Participants who reported regular aspirin use, equal to or more than twice a week, were older, more likely to have smoked, used multivitamins and folate, and consumed slightly more alcohol.

In an average-risk population of men, results showed that the benefit of aspirin was not apparent until after more than five years of use. The greatest reduction in risk was observed at cumulative doses of more than 14 standard tablets (325 mg) per week, which is higher than normally recommended. The benefit of aspirin use appears to diminish less than four years after stopping use and is not evident after four to five years of discontinued use.

The Health Professionals Follow-up Study has been conducted on 51,529 U.S. male dentists, optometrists, osteopaths, podiatrists, pharmacists and veterinarians, who returned a mailed health questionnaire in 1986. The questionnaire included questions about diet, aspirin use and medical diagnoses, including cancer. The biennial questionnaires ask for updated information including cancer diagnoses and aspirin use. The participants were between 40 and 75 years of age when the study began.

This year an estimated 147,000 Americans will be diagnosed with colorectal cancer and 56,500 will die from this disease, with an approximate 1-in-18 lifetime probability of developing colorectal cancer.

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