[ RadSafe ] Can you catch cancer?

[Dawson, Fred Mr]

This is an interesting report in the Guardian newspaper which offers an
explanation for cancer clusters that many ascribe to man-made
environment, assuming that fallout from a power station or radiation
from a phone mast must be to blame. 

http://www.guardian.co.uk/medicine/story/0,,1693469,00.html

"In the early 1980s, US doctors began to notice a strange phenomenon. A
rare form of cancer, once confined to elderly Jewish men in Europe, was
suddenly cropping up among young gay men. The explanation? By catching a
new virus, called HIV, they were also developing cancer. Now doctors
believe that other infections, even simple coughs and colds, can trigger
everything from childhood leukaemia to cervical cancer. Should we be
worried? Sarah Boseley investigates 

Within a few years, girls will be vaccinated against cancer. Not every
cancer - at least, not yet. But the cervical cancer jab is well on its
way. There are currently 3,000 new cases of cervical cancer a year in
the UK. A couple of shots in the arm, perhaps, and young women may never
have to think about it again.
 
That is possible because cervical cancer is spread by a virus called
HPV, or human papilloma virus. You can catch it by sleeping with
somebody who has it, so women with more sexual partners are more likely
to get it. The vaccine does not act against cancer per se, but protects
against the virus which causes it. Which makes cervical cancer,
effectively, an infectious disease.

Can you really catch cancer? And if cervical cancer is caused by an
infection, is it remotely possible that we might also catch breast
cancer, or prostate cancer, or bowel cancer? The answer is yes and no.
Certainly, catching cancers is not the same as catching a cold. Human
papilloma virus may trigger cervical cancer, but many women infected
with it will never develop the disease. There must also be other
factors. 

Where a virus is involved in cancer, it appears, it is one of many
causes - a trigger in a chain of triggers. Along with the virus, there
may have to be something in your genes that tips your chances of getting
this particular cancer the unlucky way. Diet affects some cancers,
alcohol others, smoking is an important risk factor and air pollution is
under suspicion. But the remarkable and exciting thing about the
involvement of viruses in cancer is that they are a switch that can
potentially be turned off. This is not a bad news story; quite the
opposite. If an infection is involved in the onset of some cancers, then
there is a way to stop them developing. Potentially, we could invent a
vaccine. That is exactly what has happened in cervical cancer and there
is every reason to think that, one day, it may be possible in other
cancers too. 

We do not know to what extent viruses are implicated yet, nor in which
cancers, but the estimate is that they may play a part in up to 20% of
cases. The evidence is slowly accumulating. Just before Christmas, a
paper appeared from Newcastle University that offered new evidence that
minor viral infections such as colds, respiratory problems and mild flu
might trigger childhood cancer. Richard McNally, an epidemiologist, had
mapped outbreaks of two cancers - forms of leukaemia and brain tumours -
in children under 15 over a period of 45 years from a tumour database in
Manchester. He discovered clusters of children who were born around the
same time and in the same place - and went on to develop cancer. 

Whenever clusters of childhood cancers have been spotted, parents have
understandably ascribed them to the man-made environment, assuming that
fallout from a power station or radiation from a phone mast must be to
blame. But McNally and colleagues have identified a pattern which is
exactly like what you would see in infectious diseases. 

"We found that place of birth was particularly significant, which
suggests that an infection in the mother while she is carrying her baby,
or in a child's early years, could be a trigger factor for the cancer,"
says McNally. "These could be minor common illnesses that are not even
reported to the GP, such as a cold, mild flu or a respiratory virus."
But no, he hastens to say, you cannot catch cancer. His research
suggests that infection is one of the factors in its onset, but it is
not the only cause. 

Instead, the hypothesis that his research helps to support is a
double-whammy theory. Firstly, babies are born with a propensity to
leukaemia. Mel Greaves, a professor at the Institute of Cancer Research
in London, analysed the blood taken by midwives from the heel-pricks of
newborns and found that many already have cell damage that could lead to
the disease. But it is now clear that a second thing has to go wrong
before a possibility becomes a likelihood. And that could be a viral
infection. 

This fits with the work of Leo Kinlen at Oxford University, who has been
lambasted by anti-nuclear campaigners for his theory, first mooted in
1988, that childhood leukaemia is not the result of radioactive fallout
and waste but caused by "population mixing". Cancer clusters occur where
whole groups from towns and cities have arrived to live and work in a
remotish rural setting, he observed. Look at the oil fields, military
installations, the building of new towns - and nuclear plants too. The
incomers bring with them new viral infections, which could spark cancers
among the native local population. 

In fact, infections associated with cancer have been known for some
time. There is a cat virus which causes leukaemia and a vaccine against
it, causing people to wonder if there could be a parallel in human
leukaemia. But the neatest example of infection as a significant cause
is in stomach cancer. This is not triggered by a virus, but by a
bacterium called Helicobacter pylori. That discovery netted a recent
Nobel prize. "Fifteen to 20 years ago," says Heather Dickenson,
principal research associate at Newcastle University's centre for health
services research, "nobody would have taken seriously the theory that
stomach cancer was the result of infection." 
Helicobacter pylori is a bacterium that enters the stomach in food and
drink, but does not get destroyed by the acid there. Around 30-40% of us
are thought to be infected with it, and it can cause inflammation of the
stomach lining, known as gastritis. In a small number of cases (about
3%, which means that other triggers such as diet or smoking have to be
involved) that progresses to stomach cancer. But now we know that H.
pylori is one of the guilty parties, many of these cancers (though not
all) can be prevented. Give patients the right antibiotics, and H.
pylori goes away. 

Research into the links between cancer and viruses began around the
start of the last century. In 1908, two Danes, Wilhelm Ellermann and
Oluf Bang, identified a virus which they found spread leukaemia between
chickens. In 1911, Peyton Rous in the United States found another
chicken virus which caused sarcoma. The work was ignored for decades,
but eventually won Rous a Nobel prize in the 1960s. 

In that same decade, the first definitive link between infection and a
human cancer was established. A British scientist called Anthony
Epstein, based at the Middlesex hospital, went to listen to a British
surgeon called Denis Burkitt, who had identified what is now known to be
the commonest childhood cancer in Africa. This was a tumour of the jaw
that became known as Burkitt's lymphoma. 
In a remarkable piece of scientific detective work, Epstein mapped the
incidence of the tumour across the wet, lowland areas of central Africa
and realised he was looking at the malarial belt. He hypothesised that
the cancer was caused by an infectious agent, spread by the malarial
mosquito, and spent two years staring down an electron microscope
attempting to find it. 
He and his team had no luck until one tumour biopsy arrived from Uganda
in an unfit state for microscopic examination. So Epstein cultured the
cells instead. To everyone's surprise, it grew a previously unknown form
of herpes virus, which became known as Epstein-Barr. Epstein-Barr was
later found in almost all samples of Burkitt's lymphoma from Africa. 

Almost everyone has this virus. "Ninety-five per cent of us are infected
by Epstein-Barr," says Lawrence Young, professor of cancer biology at
the institute of cancer research in Birmingham. "It doesn't cause us any
effect at all. But with certain co-factors it could cause problems."
Malaria was a co-factor in Africa, which is why the pattern of incidence
of Burkitt's lymphoma matched the malarial regions. 

The ultimate proof that a virus is a contributory cause of cancer is if
you remove it, says Young. "Hepatitis B virus is associated with primary
liver cancer. It's very common in Africa and the Far East. About 25
years ago they introduced a vaccine for Hepatitis B in Taiwan where it
had been a very common infection and you would see liver cancer in young
adults. The incidence of liver cancer in the population has been
significantly reduced." 

If you have Epstein-Barr and you catch malaria while on holiday, it does
not mean you will develop Burkitt's lymphoma. None of this is quite that
simple. You would have two of the risk factors - two possible triggers -
but because this is mostly an African cancer, there is probably a
genetic component involved too. Too little is known about the causes of
cancer, for all the noise made about diagnosis and treatment. But if
scientists can nail down a particular virus as a risk, they can
interrupt the process that can cause disease and death. Young calls the
virus "a link in the chain of events. This is not like catching a cold.
You can't catch cancer as an acute disease. But if it is a vital link,
you can break the chain." 

Epstein-Barr is also implicated in about half of Hodgkin's lymphomas,
but not the other half. In China, Epstein-Barr is in nasopharyngeal
carcinoma - but fascinatingly, the extra link in the chain is the salted
fish in the Cantonese diet (and probably some genetic propensity as
well). "We know because if populations from China move to the west coast
of America, in one generation they lose it," says Young. "It's the
changes in their diet." Breast cancer, too, appears to have dietary
links. The incidence in Japanese women who move to the US soars. "Diet
is a major contributory factor to cancer," acknowledges Young. 

Diet we can change. Viruses and bacteria we live with, for the most part
harmoniously as long as our bodies' infection-fighting systems are in
good order. Epstein-Barr does most of us no harm unless our immune
system is suppressed. In the early days of heart transplants, for
instance, most patients died not because the heart gave out or was
rejected, but of Epstein-Barr-associated lymphomas. They were being
given massive doses of immuno-suppressant drugs, which meant that the
virus was no longer kept in check, allowing the cancer to develop. 

And in the early 80s, the first sign that we were in trouble from a new
virus that would wreak havoc across the planet was the arrival of a new
cancer in America called Kaposi's sarcoma. It had once been a very rare
disease in elderly Jewish men from the Mediterranean. Suddenly, young
gay men had it, as the HIV virus knocked out their immune systems,
allowing the Kaposi's sarcoma herpes virus to flourish. 

Viruses are now thought to be implicated in up to one in five cancers.
As time goes on, we may find it is more. There are some controversial
theories around. Papers have been written that suggest a monkey virus
called SV40 is a trigger, with asbestos, for mesothelioma - a cancer of
the lining of the chest wall, the abdominal cavity or the lining of the
heart. Some have speculated that the monkey virus may have passed to
humans through contaminated stocks of polio vaccine. Others are looking
for a virus in lung cancer. In Australia, researchers are studying a
human virus similar to one called MMTV which is responsible for mammary
tumours in mice. They want to know if it could be implicated in breast
cancer. 

Finding any cause of cancer - even one that plays a small part - is very
good news because it means prevention is possible. If a virus is
involved, it opens up the possibility of a vaccine to disrupt the chain
of events that leads to cancer. That is, in short, a holy grail. The
revelations of the excellent results in trials of the cervical cancer
vaccine were greeted with euphoria. Gardasil, manufactured by Merck, was
100% effective among the 12,000, mostly young, women who took part. It
knocked out the two strains of HPV, 16 and 18, that are implicated in
70% of cervical cancers. 

And the vaccine could prove even more useful. The trials showed that
some of the other HPV types which are involved in a minority of cervical
cancers were also stopped in their tracks. "Because there are beginning
to be signs of cross-protection against other HPV types, [the proportion
of cancers affected] could go up," says Anne Szarewski, a clinical
consultant for Cancer Research UK who has been involved in the trial.
She thinks the proportion of cancers affected could eventually be as
high as 80%. At that point, the vaccine becomes more effective as a
prevention tool than the cervical screening programme. As newer vaccines
are developed, it is assumed they may hit the rest of the troublesome
HPV types too. 

So cervical cancer could, in theory, be wiped out, just as smallpox was.
This is unlikely to happen, however, since it is only achievable if
every girl and boy in the country has the jab. The vaccine is expected
to be offered to sexually inexperienced girls who will not have HPV,
aged around 10 to 13, but suggesting a vaccination for a young girl that
will protect her from a sexually transmitted disease has not gone down
well with parents. The Merck vaccine, unlike its GlaxoSmithKline rival,
protects also against two types of HPV that cause genital warts. "It has
proved a nightmare to promote in the States," observed Szarewski. Trials
in women over 25 who will have the virus - for most pick it up at some
point - are only just beginning. 

Cancer is the scourge of our times, the most feared disease of the 21st
century. It appears to come from nowhere and kill at random. The more we
know of the causes, the better we will be able to protect ourselves. At
the moment, the best advice we have is generally to live well - to eat a
lot of fruit and vegetables, drink in moderation, stop smoking and take
exercise. But there are plenty of people who have lived unimpeachably
healthy lives and died of cancer. Finding a silent trigger such as a
virus that scientists may be able to knock out of the equation with a
vaccine is not a reason to panic, but a cause for hope."

------------------------------------

Fred Dawson



Fwp_dawson at hotmail.com