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Mao
Jia-Ying
VIRUS AND CANCER
Around 5% of
all
human
cancers
are
found
to
be related to
viruses
-
Burkitt's lymphoma, cancers
ol
the
nose,
neck of the
womb, and
liver etc.
Cancerous change is an exceptional
event of
viral
infection
and
it
takes many
years
as well
as
involving a very com-
plex chain of events requiring the pres-
ence of several other important co-fac-
tors
in
susceptible individuals, before
cancers
can ever
be
formed.
As
chronic
viral hepatitis may lead
to
liver cancer,
it
is important
to recognize
its route
of
transmission
-
through the blood
and
sexual
contact.
Human papilloma vi-
rus
that causes cancer
of
the neck of
the
womb spread through
sexual
contact.
AIDS
viruses spread
like
hepa-
titis viruses
but
cause cancer
through
a
unique
way
-
profound
immune
suppression.
Otherwise, these viruses
have
such
common occurrence that
vast majority
of
the population are
al-
ready
exposed.
Hence, these cancers
are not considered as
"infectious".
Ei-
ther
DNA
or
RNA viruses are involved.
DNA
viruses,
e.9.,
the
Herpes
viruses
that are related to nose cancer, have a
"universal" occurrence
-
the whole
adult
population have already been exposed
but activation by "co-factors" like car-
cinogens
(oancer
causing
chemicals),
e.9., nitrosamines
are
required in
sus-
ceptible
individuals.
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