BCPA Journal - Issue 184 - British Cardiac Patients Association

6
Aspirin also helps cancer prevention
A summary by Richard Maddison of research by Peter Rothwell*
Readers may remember the article on Peter
Rothwell’s work on how Intermittent high
blood pressure predicts troubles, in the
BCPA Journal for June/July 2010. 4
His recent research findings 1,2,3 hit the
headlines around 21st March 2012. Peter
gave a summary on Today on BBC Radio
4. Essentially low-dose aspirin given daily
to heart patients for five years or more
also helps ward off various cancers –
especially of colon.
The Daily Mail quoted Peter as follows. 5
‘As a father of three young daughters all
aged under ten, I try to look after my health,
and taking a daily aspirin is an important
part of this. I take a low-dose pill, which
is equivalent to a so-called junior aspirin
(75mg a day rather than the usual painkilling
dose of 300mg). I’ve been doing this
for a few years. I know about the possible
side effects, but the evidence suggests the
advantages of taking aspirin are greater than
the disadvantages in my case.
‘I don’t have a history of indigestion,
which would otherwise make me more
susceptible to gastrointestinal bleeding.
The risk of a bleed reduces if someone has
been taking aspirin for three years anyway,
probably because those at risk have already
stopped taking the pill by then.
‘Cancer becomes more common in
people aged 50 and over, and so it might
make sense to start taking aspirin as a
preventive treatment in the late 40s, and to
stop at around 65, when the risk of bleeding
increases.
‘I don’t want to suggest that people rush
out and buy aspirin, but I think it’s at least
worth thinking about for healthy, middleaged
people like me.’
Heart disease benefits known
The benefits of low-dose aspirin to patients
who have had heart disease were already
well established.
A research trial published in 1974 found
that patients who had already had a heart
attack had lower risks of dying or further
heart troubles if they took low-dose aspirin 6 ;
and many subsequent published results have
confirmed that 7 .
Findings are for heart patients, not
general population
The findings below 1,2,3 are not based on
the general population. They come from
analysis of trials of aspirin on patients who
already had some history of heart disease
or other vascular disease. [Vascular means
involving blood flow in arteries and veins].
Thus they don’t suggest that aspirin would
be of benefit to the general population as a
primary prevention to reduce the future risk
of cancers among those that are healthy.
[Primary prevention means trying to prevent
a disease before it happens.]
Cancer risks reduced
Daily aspirin was already known to reduce
the long-term risk of death due to cancer as
well as to heart and circulation. However,
the short-term cancer effects are less certain,
especially in women. The effects of aspirin
on cancer incidence are largely unknown.
The time-course of cancer risks and benefits
in primary prevention were unclear. 1
Peter Rothwell and his team studied
cancer deaths in all trials of daily aspirin
versus control; and the time-course of effects
of low-dose aspirin on cancer incidence
and other outcomes in trials in primary
prevention. 1 [Here control means that the
patients were randomly allocated either to a
group who received aspirin or to a control
group who received a placebo dummy pill.]
The team studied individual patient data
from randomised trials of daily aspirin
versus no aspirin in prevention of vascular
events. Death due to cancer, all non-vascular
death, vascular death, and all deaths were
assessed in all eligible trials. In trials of
low-dose aspirin in primary prevention, the
team also established the time course of
effects on incident cancer, major vascular
events, and major extra-cranial bleeds,
with stratification by age, sex, and smoking
status. 1
The team’s work brought together various
previous randomised controlled trials and
found patterns. In 34 such trials involving
data on 69,224 participants, allocation to
aspirin reduced cancer deaths over five
years or more. In 51 such trials there were
also fewer non-vascular deaths overall. 1
The reduced risk of major vascular events
and of cancer by taking aspirin was initially
offset by an increased risk of major bleeding,
but effects on both outcomes diminished
with time, leaving only the reduced risk of
cancer from 3 years onwards. Patient deaths
from major extra-cranial bleeds were also
lower on aspirin than on control. 1
Alongside the previously reported
reduction by aspirin of the long-term risk
of cancer death, the short-term reductions
in cancer incidence and deaths and the
decrease in risk of major extra-cranial bleeds
with extended use, and their low patient
deaths, add to the case for daily aspirin in
prevention of cancer. 1
Malignant tumours
Daily aspirin as given to heart patients also
reduces the long-term incidence of some
adenocarcinomas. 2 [Adenocarcinoma is
a malignant tumour in glandular tissue –
breast cancers are often adenocarcinomas].
But the effects on mortality due to some
cancers appear after only a few years,
suggesting that it might also reduce growth
and/or metastasis. 2 [Metastasis means the
spread of a cancer from the original tumour
to other parts of the body by tiny clumps of
cells carried by the blood or lymph.]
The team established the frequency of
distant metastasis in patients who developed
cancer during trials of daily aspirin versus
control. 2
Allocation to aspirin reduced the risk
of distant metastasis on all cancers taken
together; adenocarcinoma; and other solid
cancers – due mainly to a reduction in
the proportion of adenocarcinomas that
had metastatic versus local disease. 2 The
effects were independent of age and sex, but
absolute benefit was greatest in smokers. 2
That aspirin prevents distant metastasis
could account for the early reduction in
cancer deaths in trials of daily aspirin
versus control. This finding suggests that
aspirin might help in treatment of some
cancers and provides proof of principle for
pharmacological intervention specifically to
prevent distant metastasis. 2
Colon and rectum cancer from 20year
studies
By 2007 researchers knew that high-dose
aspirin (≥500mg daily) reduces long-term
incidence of colon or rectum cancer, but
adverse effects might limit its potential for
long-term prevention. In 2010 the long-term
effectiveness of lower doses (75–300mg
daily) was still unknown. The team assessed
the effects of aspirin on incidence and
mortality due to colon and rectum cancer in
relation to dose, duration of treatment, and
site of tumour. 8
The team followed up four randomised
trials of aspirin versus control in primary
and secondary prevention of vascular events
and one trial of different doses of aspirin. 8
[Secondary prevention is to try to stop a
disease getting worse, or at least slow down
its progress.]
By analysis of pooled individual patient
data, the team established the effect of
aspirin on risk of colon and rectum cancer
over 20 years (mean 18.3) during and after
the trials. They found that those taking
aspirin averaged overall had reduced 20year
risk of colon cancer, but not of rectal
cancer. 8 Also 30mg aspirin daily didn’t help
prevent colon or rectum cancer.
Benefits increased with longer treatment.
Aspirin taken daily for at least 5 years at