1. Alternate day aspirin therapy was associated with neither net health benefit nor detriment for CVD and cancer in the majority of women in light of increased risk of gastrointestinal bleed.
2. However, the number needed to treat to avoid one cardiovascular event was 29 in women greater than 65 years, suggesting a greater effect of age-based aspiring prescription.
Evidence Rating Level: 2 (Good)
Study Rundown: Low dose daily aspirin has traditionally been prescribed for its benefits towards reducing the risk of cardiovascular events. Recently, evidence supporting the benefits of aspirin on the reduction of cancer risk, specifically colorectal cancer, has emerged. This study followed patients from the Women’s Health Study (WHS), a randomized trial studying the effects of alternate-day 100mg aspirin therapy on cardiovascular disease (CVD) and cancer risk in healthy women over the age of 45 years, to assess the 15-year absolute risk reduction (ARR) of CVD as well as cancer. While there seemed to initially be marginal benefit to aspirin treatment the findings did not support significant net benefit for decreased CVD risk, colorectal cancer, or non-colorectal cancer due to increased risk of gastrointestinal (GI) bleed in some women. However, findings of this study suggest a benefit of alternate-day aspirin therapy for reducing the risk of having an event in women greater than 65 years, despite their increased risk of developing a GI bleed.
Women enrolled in the WHS study were found to be at a generally lower risk for CVD as well as cancer and, as a result, may skew the external validity of this study. Further, these findings may not apply to the use of daily aspirin therapy as previous studies have found that effects of daily aspirin on cancer risk occurred sooner than those found with alternate-day therapy. Despite these limitations, the study provides credence to the conversation concerning selective age-based aspirin treatment.
Relevant Reading: Effect of daily aspirin on long-term risk of death due to cancer
In-Depth [retrospective cohort]: This study evaluated the effect of alternate-day 100mg aspirin therapy on the 15-year risk of developing CVD, colorectal cancer, and non-colorectal cancer using data from 27,939 women who had previously been enrolled in the WHS study. The participants had a median 15-year predicted risk of 1.5% for CVD, 0.5% for colorectal cancer and 8.7% for non-colorectal cancer. Therapy was associated with minimal benefit for the 15-year risk of CVD and colorectal cancer. The 15-year ARR associated with decreased CVD risk was found to be 0.27%, 95% CI 0.06% to 0.86%, number needed to treat (NNT) 371 and the same for colorectal cancer was found to be 0.14%, 95% CI 0.02% to 0.59%, NNT 709. Aspirin therapy was found to have no effect on non-colorectal cancer with a 15-year absolute risk increase (ARI) of 0.08%, 95% CI of -0.64% to 0.80%, number needed to harm (NNH) of 709. The ARI for GI bleed on aspirin therapy was 0.75%, 95% CI 0.50% to 1.00%, NNH 133. Aspirin therapy was associated with a protective effect on CVD in women greater than 65 years with a 15 year ARR of 3.11%, 95% CI 1.67%to 5.27%, NNT 29 although there was a concomitant increase in the risk of GI bleed.
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