Short-term effects of daily aspirin on cancer incidence, mortality, and non-vascular death: analysis of the time course of risks and benefits in 51 randomised controlled trials
It’s been covered at the BBC, here. They say that
“Taking a low (75-300mg) daily dose of the drug appeared to cut the total number of cancer cases by about a quarter after only three years – there were nine cancer cases per 1,000 each year in the aspirin-taking group, compared with 12 per 1,000 for those taking dummy pills.
It also reduced the risk of a cancer death by 15% within five years (and sooner if the dose was higher than 300mg)
And if patients stayed on aspirin for longer, their cancer death risk went down even further – by 37% after five years.”
This is the relevant bit from the paper
“Allocation to aspirin reduced cancer deaths (562 vs 664 deaths; odds ratio [OR] 0·85, 95% CI 0·76–0·96, p=0·008; 34 trials, 69 224 participants), particularly from 5 years onwards (92 vs 145; OR 0·63, 95% CI 0·49–0·82, p=0·0005), resulting in fewer non-vascular deaths overall (1021 vs 1173; OR 0·88, 95% CI 0·78–0·96, p=0·003; 51 trials, 77 549 participants). In trials in primary prevention, the reduction in non-vascular deaths accounted for 87 (91%) of 96 deaths prevented. In six trials of daily low-dose aspirin in primary prevention (35 535 participants), aspirin reduced cancer incidence from 3 years onwards (324 vs 421 cases; OR 0·76, 95% CI 0·66–0·88, p=0·0003) in women (132 vs 176; OR 0·75, 95% CI 0·59–0·94, p=0·01) and in men (192 vs245; OR 0·77, 95% CI 0·63–0·93, p=0·008). The reduced risk of major vascular events on aspirin was initially offset by an increased risk of major bleeding, but effects on both outcomes diminished with increasing follow-up, leaving only the reduced risk of cancer (absolute reduction 3·13 [95% CI 1·44–4·82] per 1000 patients per year) from 3 years onwards. Case-fatality from major extracranial bleeds was also lower on aspirin than on control (8/203 vs 15/132; OR 0·32, 95% CI 0·12–0·83, p=0·009).”
I have cut and pasted the numbers below.
It seems that, at 5 years, 1.42% of the the control group had cancers, and 2.94% if the control group. This is a difference, small to an individual, potentially large to a population. But we really need to know about all cause mortality – if all we are doing is reducing cancer incidence by increasing bleeding risk (eg brain haemorrhage) we might not be doing a great deal of good.
This is a very important sentence:
“Allocation to aspirin reduced the risk of non-vascular death in the 51 trials (1021 vs 1173 deaths; OR 0·88, 95% CI 0·78–0·96, p=0·003; 152 deaths avoided in 40 269 participants allocated aspirin; table 1). The proportion of deaths classed as non-vascular varied (heterogeneity p<0·0001), ranging from 10–20% in early, predominantly high-dose trials in patients with ischaemic heart disease to about 70% in predominantly low-dose trials in primary prevention (data not shown). In 12 trials in primary prevention (figure 1), , , , ,, , , , , ,  and  aspirin reduced non-vascular death (OR 0·88, 95% CI 0·78–0·98, p=0·02; 87 deaths avoided), but not vascular death (OR 0·99, 95% CI 0·87–1·12, nine deaths avoided), such that the effect on all-cause mortality was non-significant (1165 vs 1261 deaths; OR 0·92, 95% CI 0·85–1·00, p=0·06).”
Repeat: the effect on all cause mortality was not significant.
I think we need to discuss this better – rather a lot of people need to be treated with aspirin to prevent cancer, and we don’t know that this will reduce overall death rates.
I need to read the other two papers, but busy day today.