Low-Dose Aspirin May Protect Against Colorectal Cancer

Laurie Barclay, MD

September 21, 2010

September 21, 2010 — Low-dose aspirin (75 mg/day) may protect against colorectal cancer, according to the results of a case-control study reported online September 15 in Gut.

"Previous studies have shown that aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) lower colorectal cancer (CRC) risk," write Farhat V. N. Din, from the University of Edinburgh, Edinburgh, United Kingdom, and colleagues. "However, the lowest effective NSAID dose, treatment duration, and effects on survival are not defined. In a large population-based case-control study, we have explored the relationship between NSAID dose and duration, CRC risk and overall CRC-specific survival."

The study sample consisted of 2279 patients with colorectal cancer and 2907 control subjects who completed food frequency and lifestyle questionnaires. NSAID use was defined as taking more than 4 tablets per week for more than 1 month and was classified as low-dose aspirin (75 mg), nonaspirin NSAIDs, and any NSAID. Logistic regression models allowed calculation of odds ratios (ORs) with adjustment for potential confounding variables, and log-rank tests and Cox hazard models allowed estimation of the effect of NSAID use on all-cause and colorectal cancer-specific mortality.

Low-dose aspirin use was reported by 354 patients (15.5%) and 526 control subjects (18.1%). A reduced risk for colorectal cancer, seen in low-dose aspirin users (OR, 0.78; 95% confidence interval [CI], 0.65 - 0.92; P = .004), was apparent after 1 year and was greater with increased duration of use (P for trend = .004). Use of any NSAID or nonaspirin NSAIDs was also inversely associated with colorectal cancer risk. There was no apparent effect of NSAIDs on all-cause survival duration (hazard ratio, 1.11; P = .22; 95% CI, 0.94 - 1.33) or colorectal cancer-specific survival duration (hazard ratio, 1.01; P = .93; 95% CI, 0.83 - 1.23).

"This is the first study to demonstrate a protective effect against CRC associated with the lowest dose of aspirin (75 mg per day) after only 5 years use in the general population," the study authors write. "NSAID use prior to CRC diagnosis does not influence survival from the disease."

Limitations of this study include potential recall bias; inability to determine if patients continued to take NSAIDs after diagnosis; and lack of outcome measure, which reflects plasma levels of NSAIDs ingested.

"[H]igh aspirin doses are not required for protection against CRC and ... while protection increases with duration of use, there are effects apparent within 5 years," the study authors conclude. "This effect is apparent as early as 1 year but increases with time up to 10 years. Moreover, our results are applicable to the general population and not just high-risk groups."

Cancer Research UK, Scottish government Chief Scientist Office, Medical Research Council, and Centre Grant from CORE as part of the Digestive Cancer Campaign supported this study. The study authors have disclosed no relevant financial relationships.

Gut. Published online September 15, 2010. Abstract

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