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Colorectal Cancer Prevention (PDQ®): Prevention - Health Professional Information [NCI] - Description of the Evidence

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In the Physicians' Health Study, 22,000 men aged 40 to 84 years were randomly assigned to receive placebo or ASA (325 mg every other day) for 5 years. There was no reduction in invasive cancers or adenomas at a median follow-up of 4.5 years.[58] In a subsequent analysis of more than 12 years, both randomized and observational analyses indicated that there was no association between the use of ASA and the incidence of CRC. The low dose of ASA and the short treatment period may account for the null findings.[59]

In a randomized study of 635 patients with prior CRC (T1–T2 N0 M0) who had undergone curative resection, ASA intake at 325 mg/day was associated with a decrease in the adjusted RR of any recurrent adenoma as compared with the placebo group (0.65; 95% CI, 0.46–0.91) after a median duration of treatment of 31 months. The time to detection of a first adenoma was longer in the ASA group than in the placebo group (HR for the detection of a new polyp, 0.54; 95% CI, 0.43–0.94, P = .022). Harms of treatment included upper gastrointestinal hemorrhage and hemorrhagic stroke.[60] In a study of 1,121 patients with a recent history of colorectal adenomas, after a mean duration of treatment of 33 months, the unadjusted RRs of any adenoma (as compared with the placebo group) were 0.81 in the 81-mg ASA group (95% CI, 0.69–0.96) and 0.96 in the 325-mg ASA group (95% CI, 0.81–1.13). For advanced neoplasms (adenomas measuring at least 10.0 mm in diameter or with tubulovillous or villous features, severe dysplasia, or invasive cancer), the RRs were 0.59 (95% CI, 0.38–0.92) in the 81-mg ASA group, and 0.83 (95% CI, 0.55–1.23) in the 325-mg ASA group.[61] Harms of treatment were similar in the two groups and included upper gastrointestinal bleeding and hemorrhagic stroke.

Four reports in 2007, 2010, 2011, and 2012 [57,62,63,64] have analyzed long-term follow-up of RCTs of daily ASA versus the control. The 2007 analysis reported on two RCTs with reliable follow-up of more than 20 years. This report found that the use of 300 mg or more of ASA per day for at least 5 years reduced the incidence of CRC after a latency of 10 years (RR at 10–19 years [0.60; 95% CI, 0.42-0.87]). The 2010 analysis analyzed long-term follow-up data from four RCTs, finding that allocation to ASA for 5 or more years reduced the 20-year incidence and mortality of proximal colon cancer (adjusted incidence HR = 0.35; 95% CI, 0.20–0.63; adjusted mortality HR = 0.24; 95% CI, 0.11–0.52) and also reduced the 20-year risk of rectal cancer (RR = 0.58; 95% CI, 0.36–0.92) but not distal colon cancer. There was no increase in benefit at doses more than 75 mg/day. The absolute 20-year risk reduction in fatal CRC was 1.76% (95% CI, 0.61–2.91).

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Last Updated: February 25, 2014
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