What’s the Connection?

The mechanism by which aspirin may prevent cancer is still a matter of speculation. Colorectal adenomas overexpress cyclooxygenase-2 (COX-2), one of the primary targets of aspirin and other NSAIDs, but whether blocking COX-2 inhibits adenoma growth is unknown.15 Another potential mechanism involves aspirin’s mediated inhibition of platelets, which plays an important role in blood-borne metastasis.13


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Implications for Practice

With this large body of evidence in hand, is it time to recommend daily aspirin to reduce cancer risk? Not yet. As Chan and Cook point out in an editorial in The Lancet, too many questions remain unanswered.16 The Oxford researchers relied on observational research and did not include data from two of the largest studies of aspirin use, the Women’s Health Study and the Physician’s Health Study, which used alternate-day aspirin and found no reduction in cancer risk.16 Moreover, the trials they included had cardiovascular, not cancer, endpoints. It is possible that bleeding or anemia due to aspirin therapy prompted diagnostic investigations that led to polyp removal and, thus, reduced incidence of cancer.16 With strong evidence that aspirin reduces the risk of colorectal cancer in persons with Lynch syndrome, a recommendation that these patients take prophylactic aspirin may be justified.11,16 Use of aspirin by persons with a history of colorectal cancer or for primary prevention should await the results of prospective trials with cancer endpoints.16


References

1. Murphy SL, Xu J, Kochanek KD; Division of Vital Statistics. National Vital Statistics Reports. Deaths: Preliminary Data for 2010. Natl Vital Stat Rep. 2012;60(4):1-68.

2. Chan AT, Giovannucci EL. Primary prevention of colorectal cancer. Gastroenterology. 2010;138(6):2029-2043.e10.

3. Benamouzig R, Deyra J, Martin A, et al. Daily soluble aspirin and prevention of colorectal adenoma recurrence: one-year results of the APACC trial. Gastroenterology. 2003;125(2):328-336.

4. Sandler RS, Halabi S, Baron JA, et al. A randomized trial of aspirin to prevent colorectal adenomas in patients with previous colorectal cancer. N Engl J Med. 2003;348(10):883-890.

5. Baron JA, Cole BF, Sandler RS, et al. A randomized trial of aspirin to prevent colorectal adenomas. N Engl J Med. 2003;348(10):891-899.