NMA: Nonprescription Medicines Academy

Daily Aspirin for Cancer Prevention?

May 1st, 2012

Two studies by Rothwell and colleagues add to the growing body of evidence supporting a role for aspirin in the prevention and treatment of cancer. Both studies were made available as early release Lancet articles on March 20, 2012.

Study 1
The first study analyzed all available individual patient data from randomized trials of daily aspirin versus no aspirin in prevention of vascular events, including trials in the Antithrombotic Trialists’ Collaboration. The authors assessed death due to cancer, all nonvascular death, vascular death, and all deaths in all eligible trials. In trials of low-dose aspirin in primary prevention, the authors also established the time course of effects on incident cancer, major vascular events, and major extracranial bleeds, with stratification by age, sex, and smoking status.

In 51 trials involving more than 77,000 participants, men and women treated with aspirin had fewer deaths from nonvascular causes (1,021 vs 1,173; OR, 0.88; 95% CI, 0.78–0.96; p = 0.003). This was due mainly to reduced cancer deaths among 69,224 participants in 34 trials (562 vs 664 deaths; OR, 0.85; 95% CI, 0.76–0.96; p = 0.008), particularly from 5 years onwards (92 vs 145; OR, 0.63; 95% CI, 0.49–0.82; p = 0.0005). In primary prevention trials, the reduction in nonvascular deaths accounted for 91% of deaths prevented.

In six trials of daily low-dose aspirin in primary prevention involving 35,535 participants, men and women treated with aspirin had a reduced incidence of cancer from 3 years onwards (324 vs 421 cases; OR, 0.76; 95% CI, 0.66–0.88; p = 0.0003). The reduced incidence was independent of age, sex, and smoking status.

A reduced risk of major vascular events in participants treated with aspirin was offset initially by an increased risk of major extracranial bleeding. However, both of those effects diminished with increasing duration of trial follow-up, such that the reduced risk of cancer was the only significant effect (absolute reduction 3.13 per 1,000 patients per year; 95% CI, 1.44–4.82) from 3 years onwards.

Study 2
The second study focused on five large, randomized trials conducted in the United Kingdom that compared daily aspirin therapy (≥75 mg daily) with control for the prevention of vascular events. The trials involved a total of 17,285 participants. The objective of this study was to establish the frequency of distant metastasis in the 987 patients who had a new solid cancer diagnosed during mean in-trial follow-up of 6.5 years.

A review of electronic and paper records showed that allocation to aspirin reduced the risk of cancer with distant metastasis by 30%–40% (HR, 0.64; 95% CI, 0.48–0.84, p = 0.001). This was attributable mainly to a nearly 50% reduced risk of metastatic adenocarcinoma (OR, 0.52; 95% CI, 0.35–0.75; p = 0.0006). In patients with adenocarcinoma who did not have metastasis at initial diagnosis and who remained on trial treatment up to or after diagnosis, allocation to aspirin reduced risk of metastasis on subsequent follow-up by about 70% (HR, 0.31; 95% CI, 0.15–0.62; p = 0.0009). Aspirin also reduced the overall risk of fatal adenocarcinoma (HR, 0.65; 95% CI, 0.53–0.82; p = 0.0002). Effects were independent of age and sex, with the greatest absolute benefit seen in smokers.

According to the authors, the study findings provide proof of principle for pharmacological intervention specifically to prevent distant metastasis.

Citation for both studies: Lancet. 2012 Mar 20. [Epub ahead of print]