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- Medical scientists believe that they have found the "missing
link" between the causes of cancer and the body's immune system.
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- Following the breakthrough researchers think that they
can explain why tumours can sometimes evade the body's defences and how
existing anti-inflammatory drugs could help to fight against the disease.
According to this new view of cancer, these defences could be boosted by
regular doses of a common drug such as aspirin.
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- With around one in three people in Britain developing
cancer at some stage in their life, finding ways of treating or preventing
the disease has been the target of medical science for decades. But while
the causes of most forms of cancer are now well-recognised, only in a few
cases - such as with Tamoxifen and breast cancer - have efforts to fight
the disease been successful.
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- In theory, the body's own immune system should seek out
and destroy any cancerous cells. Such cells are constantly being created
because of genetic damage but are usually dealt with. Why this does not
always happen has, however, so far been a mystery. Now scientists in Britain
have, for the first time, tied the spread of cancer to the failure of the
immune system to stop the disease.
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- The link emerged following a lecture given last year
by Prof Angus Dalgleish, an expert on cancer and immunology at St George's
Hospital, London, to cancer researchers at Leicester Royal Infirmary. He
explained that studies of the immune systems of patients with colon cancer
had found unusually low levels of so-called Th1-type immunity, which is
involved in fighting microbes.
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- This suggested that the cancer thrived when Th1 (thymus-derived
helper cell type 1) levels were low - when, for example, the immune system
was fighting inflammatory diseases. In the audience was Dr Ken O'Byrne,
from Leicester Royal Infirmary, who was studying how tumours spread through
new blood vessels around them. He told The Telegraph: "A whole lot
of things suddenly fell into place."
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- According to Dr O'Byrne, the picture of cancer that emerges
is of a disease that starts with healthy cells being attacked for many
years by irritants such as the chemicals in tobacco smoke. This causes
long-term inflammation which, in turn, prompts the body's immune system
to switch into healing mode, lowering its Th1 level to allow repairs to
be carried out.
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- Dr O'Byrne said: "The trouble is that we need Th1
to detect and deal with invaders like viruses and bacteria, and also with
normal cells that have turned cancerous. But if Th1 levels have fallen,
it means that any cells that have become cancerous have a better chance
of evading our immune system." Worse still, the wound-healing process
triggered by inflammation is also linked to increase in the so-called Th2
response, which is responsible for creating new blood vessels around damaged
tissue.
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- Dr O'Byrne said: "This is fine if the tissue really
does need repair. But if it's actually made from cancer cells, then these
new blood vessels just allow the tumour to grow and spread around the body."
Long-term tissue inflammation thus leads to a "double whammy"
effect, said Dr O'Byrne: "Not only does the lower Th1 level allow
cancer cells to go undetected, but the increased Th2 level actually helps
them to grow and spread."
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- According to Dr O'Byrne, this new view of cancer explains
why the disease is so often linked to inflammatory disorders. "Evidence
has been accumulating for years that conditions like ulcerative colitis
and chronic hepatitis are linked to cancer in later life. Now we can explain
why. It is the response of the immune system to these inflammatory conditions
which allows cancer cells to thrive." More importantly, said Dr O'Byrne,
it points to new ways of tackling the disease. "It suggests that drugs
that fight inflammation and raise Th1 levels could help fight cancer, or
even prevent it. Aspirin is an obvious case in point."
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- According to Prof Dalgleish, there is already evidence
that taking aspirin long-term does help prevent cancer. He said: "There
are many reports that patients taking aspirin over many years really do
have a lower rate of many cancers, including colorectal, oesophageal and
lung cancer - just as this new approach would predict." Prof Dalgleish
is now working with Dr O'Byrne on a series of papers for leading medical
journals outlining the implications of the new view of cancer.
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- He said: "What we need now is a big clinical trial
to test this new approach, with thousands of patients over several years."
The findings so far have already caught the attention of other leading
cancer experts. Prof Robert Hawkins of the Christie Hospital, Manchester,
said: "It is a very interesting proposal that needs to be pursued."
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- Prof Adrian Harris of the Imperial Cancer Research Fund
unit at the Churchill Hospital, Oxford, said that by linking cancer with
inflammation the new approach may lead to more ways of stopping the spread
of cancer. He said: "To spread, tumours have got to get a blood supply
and also escape immune surveillance, so this new approach gives two routes
for dealing with that."
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- Prof Dalgleish said that a combination of anti-inflammatory
drugs and Th1 boosting agents could have a dramatic impact on the war against
cancer: "At the very least we may be looking at such a combination
helping to prevent and treat over half of all cancers." He said that
he was already sufficiently convinced of the link to have begun a regular
course of anti-inflammatory medication: "I now take at least 300mg
of dissolvable aspirin each day."
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- Prof Dalgleish said, however, that such a course should
only be undertaken under medical supervision.
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