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The role of aspirin in preventing colorectal cancer (CRC) is not completely understood. Several randomized control trials have shown that aspirin lead to reduction in the risk of recurrent colorectal adenomas in patients diagnosed with cancer or adenomas. However, the effects of aspirin on primary prevention of colorectal cancer are only recently demonstrated in a recent study by Flossmann et al (2008).
Flossmann et al. (2008) examine the effects of aspirin on colorectal cancer incidence in UK populations, enrolled in British Doctors Aspirin Trial and the UK-TIA Aspirin Trial. The follow-up time of the aspirin trials is more than 20 years. The patients in these aspirin trials are assigned to either 500 mg aspirin a day for 5 years, 300 mg or 1200 mg aspirin a day for 1-7 years, open control and placebo control arms. The study showed that aspirin leads to reduction of colorectal cancer incidence. The effects are only observed at 10 years into the trials. A consistent association of lower incidence of colorectal cancer was observed with use of 300 mg or more of aspirin a day.
Hoffmeister et al (2008) conducted a similar study for a population in Germany. They also investigated how aspirin used in combination with other drugs affect the incidence of colorectal cancer. Hoffmeister et al (2008) found a small risk reduction of CRC for regular use of low-dose aspirin (odd ratio: 0.77) and a stronger reduction with regular use of statins (odd ratio 0.65). Use of both statin and aspirin leads to a reduction of 62% after 5 or more years.
Chan et al investigated the pathway of how aspirin might reduce the risk of colorectal neoplasm. They examined the effects of aspirin on cancers that express cyclooxygenase-2 (COX-2) and cancers that do not. Aspirin use was found to substantially reduce risk of colorectal cancers that express COX-2 (odd ratio: 0.64). On the other hand, aspirin use has no effect on colorectal cancers with weak or absent expression of COX-2. The results suggested that aspirin lowering the risk of colorectal cancer through the COX-2 pathway.
In summary, use of aspirin not only prevents heart diseases but also cancer, more specifically colorectal cancer. Scientists have recently made headways in understanding the preventive effects of aspirin. We might expect new chemopreventive drugs in future based on these findings.
Hoffmeister M. Individual and joint use of statins and low-dose aspirin and risk of colorectal cancer: a population-based case-control study. Int J Cancer. 2007 Sep 15;121(6):1325-30. PMID: 17487832 [PubMed - in process
Chan AT. Aspirin and the risk of colorectal cancer in relation to the expression of COX-2. N Engl J Med. 2007 May 24;356(21):2131-42
Flossmann E; British Doctors Aspirin Trial and the UK-TIA Aspirin Trial. Effect of aspirin on long-term risk of colorectal cancer: consistent evidence from randomised and observational studies. Lancet. 2007 May 12;369(9573):1603-13. Review. PMID: 17499602