Cancer is a major killer, but its cause is still a -pestering mystery. Now a recent study linking carcinogens and human bodies at the molecular level throws some light on this dark alley
CANCER remains a mystery in its aetiology even today. Death tolls from cancer
are gaining staggering proportions; the
us recorded 538)000 deaths from cancer
in 1994, which amounts to one-fifth of
the nation's population. The basic problem in cancer research is the unavailability of conclusive causative agents
The disease finds its way into existence
out of billions of complex interactions
that make up human cellular biochemistry. Some of these causes are inherited,
like the gene BRCA- 1, which causes
breast cancer. However, there are also
many environmental factors presumably avoidable: asbestos, tobacco, air
pollution, a diet low in vegetables and
fruits, alcohol and UV-radiations.
As researchers screen out more and
more substances that have the potential
to cause cancer, there has set in a certain
cynicism about the potential hazards
of persuing one's gastronornal indulgences. Peanut butter, mustard, mushrooms, root beer-all are said to be
containing trace amounts of potential
carcinogens. This raises the concern
whether food that comes from the
kitchen may turn out to be the destroyer.
Carcinogens are normally found
through the detection of significant rise
in malignancies in animals exposed to
potentially carcinogenic test chemicals.
The virtue of this system lies in the simplicity of the procedure. Unlike people,
these laboratory animals have a rather
uncomplicated life without exposure to
thousands of foods, chemicals or
obnoxious gases in the atmosphere.
They can be subjected to carefully
designed and tightly controlled experiments and the exclusion criteria is much
more strictly regulated as compared to
test models including human specimens. In short, the outcome of animal
model studies can be confidently taken
into account as the tell-tale story that it
shows because of the lesser chances of
unpredictable causes.
Some scientists including Bruce
Ames at the University of California at
Berkeley, us, have cited differences in
'animal models and those of humans
saying that there is a vast gap between
the generic configuration of the animals
and human test systems despite the fact
that both rodents and humans are
mammals. A carcinogen mainly works
by causing a mutation in an oncogene
- a gene that, if it malfunctions, lays
the groundwork for the uncontrolled
proliferation of the cell where it resides.
Now a new development in the
field of research called 'molecular
epidemiology' addresses different questions in the sub-microscopic arena,
where cells interact with foreign
chemicals, It may even be able to establish distinction between lethal and
insignificant doses of a potential carcinogen. And ultimately, may succeed
in producing a simple blood test
which shows that you are harboring a
clinically dangerous amount of a cancer
causing substance.
Frederica Perera and her colleagues
at Columbia University began their
work with humans rather than test animals. They amassed tissue and body
fluid samples from volunteers, who
either have cancer or have been exposed
to suspect chemicals. They then combed
through these tissues for tell-tale biomarkers - the chemical products that
reveal interaction between a suspected
carcinogen and human cell. In these
cases investigators most often hunt for
an 'adduct' - a suspicious chemical
bond between the substance and human
DNA. Carcinogen adducts can be the first
stage in a process that disrupts DNA
replication during cell division. So when
an adduct forms an oncogene, the
machinery of cellular replication can
run haywire, setting the stage for malignancies. This can cause cancer. However, adducts are not the disease. Molecular epidemiologists may establish the
link between the quantity of adducts
and biomarkers in a person's tissue and
the subsequent chances of carcinoma.
The amount of personal risk can be
calculated exactly by means of a simple
blood test. If a person has high levels
of adducts and biomarkers, his exposure
to carcinogens can be restricted or
eliminated (Discover, May 1996).
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