Low-dose aspirin may protect against colorectal cancer

Aspirin may protect against development of colorectal cancer even at low doses, according to a new study.

Existing evidence indicates that nonsteroidal anti-inflammatory drugs (NSAIDs), including aspirin, can reduce risk for colorectal cancer, but the lowest effective dose, optimal duration, and effect on survival have not yet been determined. Researchers in Scotland performed a population-based case-control study to examine the relationship between colorectal cancer risk and use of NSAIDs. Cases (n=2,279) and controls (n=2,907) matched for age, sex and residential area completed questionnaires that asked about their diet and lifestyles one year before colorectal cancer diagnosis or before study recruitment, respectively. The researchers classified NSAID use as low-dose aspirin (75 mg), non-aspirin NSAIDs and any NSAID. To be considered to have used NSAIDs, cases and controls had to have taken more than four tablets weekly for more than a month. The study results were published online Sept. 15 by Gut.

Mean age was 62.2 years for cases and 62.5 years for controls. Overall, 648 cases (28.4%) and 1,025 controls (35.3%) reported taking any NSAID. Three hundred fifty-four cases (15.5%) and 526 controls (18.1%) reported taking low-dose aspirin. Use of any NSAID conferred a lower risk for colorectal cancer (odds ratio, 0.73; 95% CI, 0.64 to 0.83). For aspirin, larger doses (>525 mg/wk) were associated with the greatest risk reduction (odds ratio, 0.66; 95% CI, 0.41 to 1.05), but low-dose aspirin also had a protective effect (odds ratio, 0.78; 95% CI, 0.65 to 0.92; P=0.001). The inverse association between low-dose aspirin and colorectal cancer increased along with duration of use (P=0.004 for trend). The authors performed a cumulative dose analysis and found that risk reduction with low-dose aspirin could be detected after one year but became statistically significant after five years of consistent use. Larger doses of NSAIDs did not appear to affect all-cause or colorectal cancer-specific survival (hazard ratios, 1.11; 95% CI, 0.94 to 1.33; P=0.22 and 1.01; 95% CI, 0.83 to 1.23; P=0.93, respectively).

The authors acknowledged that they could not tell whether patients kept taking NSAIDs after a cancer diagnosis, which would limit their findings on survival, and that they did not have data on plasma levels of NSAIDs in study participants. However, they concluded that lower doses of aspirin protect against colorectal cancer and that this effect increases over time. They called for randomized, controlled trials of incident colorectal cancer to assess the possible effect of NSAIDs on survival.