Abstract and Introduction

Abstract

Daily aspirin reduced short-term risk for cancer incidence and death, and also lowered risk for metastasis.

Introduction

Previous meta-analyses of long-term follow-up data from five large randomized trials of daily aspirin for prevention of vascular events showed that, compared with placebo or no treatment, aspirin lowered colon cancer incidence and mortality after 8 to 10 years and lowered mortality from other common solid cancers after 5 to 15 years (JW Gen Med Dec 29 2011). Now, these investigators have conducted two new meta-analyses of trials of aspirin for preventing vascular events: One, designed to assess the short-term effects of aspirin on cancer incidence and mortality, included in-trial data from 51 studies that involved more than 77,000 patients — and the other, aimed at studying aspirin's effects on risk for metastasis, included data from five U.K. studies that involved more than 17,000 patients.
In the first analysis, 34 trials in which cancer deaths were reported showed that significantly fewer such deaths occurred among patients who received aspirin (odds ratio, 0.85); this benefit was most pronounced ≥5 years after randomization (OR, 0.63). In six primary-prevention trials, cancer incidence was significantly lower for patients who received aspirin (OR, 0.88), and this benefit was apparent after 3 years of follow-up. Meanwhile, aspirin's prevention of vascular events and its association with extracranial bleeds both waned, becoming nonsignificant after 3 years.
Aspirin's observed benefits after 3 to 5 years of follow-up suggest that it might inhibit metastasis, not just initial carcinogenesis. In the second meta-analysis, the investigators assessed time to diagnosis of solid cancers and identification of metastases. Aspirin slightly lowered the overall incidence of cancer; moreover, compared with cancers in the control group, more cancers in the aspirin group remained localized (OR, 1.24), whereas fewer cancers metastasized (OR, 0.64). Among patients who developed incident solid cancers, those taking aspirin were significantly less likely to have metastases at diagnosis or follow-up (OR, 0.59). This effect was significant only for colorectal cancers (OR, 0.36) and all adenocarcinomas (OR, 0.52). Among patients with initial diagnoses of localized cancer, those taking aspirin had significantly lower risk for subsequent metastasis (hazard ratio, 0.45) and better survival rates (HRs, 0.71 for cancer-related deaths and 0.81 for all-cause deaths).

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