New evidence has emerged that adds further insight into the risks and benefits of aspirin for prevention of colorectal cancer. Aspirin has been extensively studied in observational epidemiologic settings that address duration of use, dose, and magnitude of risk reduction. The observational evidence is consistent with evidence from randomized primary prevention trials, which have shown that use of at least 300 mg of aspirin per day for at least 5 years is effective in preventing colon cancer, reducing risk by about 25% (Flossmann and Rothwell 2007). A latency of about 10 years is observed. Like all chemoprevention strategies, risks and benefits must be balanced (Glasziou and Irwig 1995). To date, the risk-benefit considerations of cardiovascular disease, bleeding complications, stomach pain, and heartburn have precluded recommendations for aspirin use as a widespread prevention strategy (Gralow, Ozols et al. 2008; Cuzick, Otto et al. 2009).
In the Lancet, a new study combining data from four randomized trials of aspirin versus control in both primary and secondary prevention of vascular events evaluated risk of colorectal cancer over 20 years (study). A fifth trial compared doses of aspirin. After combining the data on individuals in these five trials the investigators observed that aspirin use reduced the 20-year risk of colon cancer but not rectal cancer. Risk of cancer was reduced by 25% and colon cancer mortality was reduced by 35%. Similar to previous reports, benefit of aspirin use increased with duration of use indicating that aspirin use operates early in the pathway to colon cancer and leading to long-term therapy as the necessary approach for prevention of colon cancer. This study, in contrast with previous evidence suggests that the benefit for colon cancer prevention is obtained with as little as 75 mg per day.
Importantly, this study separately evaluated colon cancer rectal cancers. We have previously shown that the risk factors for these two cancers sites vary substantially (Wei, Giovannucci et al. 2004). The evidence for aspirin adds further support for strategies to be specific to risk, particularly among those who are at increased risk, as is the case for family history.
Cuzick, J., F. Otto, et al. (2009). “Aspirin and non-steroidal anti-inflammatory drugs for cancer prevention: an international consensus statement.” Lancet Oncol 10(5): 501-507.
Flossmann, E. and P. M. Rothwell (2007). “Effect of aspirin on long-term risk of colorectal cancer: consistent evidence from randomised and observational studies.” Lancet 369(9573): 1603-1613.
Glasziou, P. P. and L. M. Irwig (1995). “An evidence based approach to individualising treatment.” BMJ 311: 1356-1359.
Gralow, J., R. F. Ozols, et al. (2008). “Clinical cancer advances 2007: major research advances in cancer treatment, prevention, and screening–a report from the American Society of Clinical Oncology.” J Clin Oncol 26(2): 313-325.
Wei, E. K., E. Giovannucci, et al. (2004). “Comparison of risk factors for colon and rectal cancer.” Int J Cancer 108(3): 433-442.