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Paolo
Mocarelli
Prof. Paolo Mocarelli
Univ. Dept. Laboratory Medicine
Hospital of Desio
Piazza Benefattori, 1
20033 Desio - Milano Italy
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The term cancer refers to a group of diseases in which cells
multiply and spread beyond any limit within the body.
Cancer is diagnosed in about 10 million people worldwide, and
more than 6 million die from this disease. In the United States,
the incidence rate for prostate cancer is 170 per 100,000
individuals and 135 per 100,000 for breast cancer; lung and stomach
cancer have an incidence rate of 80 in males and 50 in females.
Cancer arises from the loss of normal cell growth. This loss is
comparable to the failure of the cell�s ability to begin the
process of �apoptosis�, which is a biological program of
self-destruction. Thus, a crucial problem lies in the
identification of those agents, the so-called �cancerous agents�,
that are responsible for tumour induction.
Carcinogens act through a multiphasic process, which begins with
a series of genetic mutations and stimulates the cell toward
uncontrolled proliferation.
These phases can take decades to evolve employing a long period
of time to bring about cancer development. This is the case of the
carcinogens contained in cigarette-smoke whose action can engage
twenty to thirty years.
Since the progress of cancer requires numerous mutations, the
probability of cancer increases with increasing age; a 75 year old
has a 1,000 times greater chance for developing cancer than a 25
year old. Obviously, this is also due to the longer exposure to the
cancerous agents.
What causes cancer? Various factors: besides heredity, which
seems to be minimally involved, three main categories of elements
exist: chemical factors (smoking, diet, environment), radiation,
bacteria or viruses.
All of these contribute toward the development of cancer by
stimulating genetic modifications.
Chemical substances and radiations act by damaging genes;
viruses introduce their own genetic material into the cell;
individual hereditary predisposition transfers genetic alterations
that allow a greater susceptibility towards cancer.
These spontaneous or carcinogen-induced mutations can give rise
to three gene classes: Oncogenes, Tumour suppressor genes, and DNA
repair genes. Oncogenes are produced by mutations of
proto-oncogenes. Oncogenes encode for a modified structure or for
an excessive protein responsible for cell growth. The lack of
oncosuppressor genes, the best known being p53, can lead to tumour
development. DNA repair genes correct the errors occurring during
replication.
Here are some
examples of cancerous agents:
Cigarette smoke contains more than 24 chemical substances
capable of causing tumours. It accounts for about 30% of deaths in
the United States and is the leading cause of death from cancer
worldwide. There is a direct relationship between cancer and number
of cigarettes smoked. Some carcinogens are concentrated in certain
work environments: arsenic, asbestos, benzene, chromium,
naphthylamine, radon, vinyl chloride, and wood dust. Benzene
exposure can lead to a high risk of leukaemia.
Recently, a particular class of carcinogens has been defined:
�Endocrine Disruptor Chemicals� (EDC). These can be drugs,
pesticides, chemical contaminators, and heavy metals. They seem to
be one of the multifactorial agents involved in breast cancer. DDE
exposure, a DDT metabolite, may be associated with a high risk of
breast cancer, as also is the case with Dieldrine an
organochlorate. Dioxin also belongs to this family of compounds and
its effects have been studied in Seveso, where an increase in
colorectal cancer, lymphopoietic tissue malignancies, Hodgkin
disease, and myelogenous leukaemia, has been observed. It appears
that EDCs may be implicated in the augmented endometrial,
testicular, and prostate cancer rates.
Industrial contamination alone does not seem to be one of the
major causes of increased tumour incidence. Radio-frequency waves
along with magnetic fields do not appear to be responsible for
brain tumour development. However, radiation is known to raise
tumour rates. Ultraviolet rays increase the risk of melanoma.
There are viruses as well that are associated to human tumours.
EBV induces Burkitt�s lymphoma, HPV causes uterine cervical cancer;
HBV is responsible for liver cancer, HTL brings about T-cell
leukaemia, and Kaposi sarcoma virus determines Kaposi sarcoma.
Recently,Helicobacter pylori, a bacteria which causes peptic
ulcer, has been connected with stomach cancer.
New findings in the fields of molecular biology and genetics
have allowed the molecular characterization of tumours and the
search for new biomarkers.
The laboratory will play a major role in pharmacogenomics and in
the identification of new biomarkers.
Prevention is of primary importance. Avoid smoke-filled
environments, obesity, a sedentary life, and a meat and saturated
fats rich diet. At this moment in time, this seems to be the best
system for reducing the risk against cancer.
References
- Edwards, Richard . The problem of tobacco smoking. BMJ
2004;328(7433):217-9.
- Bognolo, Giulio editorial registrar. Calculating the risk of
disease. BMJ 2004;329(7459):237.
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