Cancer Problem
DEFINITION - CAUSES
A Simple definition of cancer is relatively autonomous growth of tissue .
A Carcinogen is an agent that causes cancers
A Carcinogen may be
1-Physical e.g Radiation
2- Chemical e.g Poly cyclic hydrocarbon
3-Biological e.g Virus
Exposures to such an agent may causes cancer either by producing direct genotoxic effects on deoxyribonucleic acid (DNA) e.g as with radiation or by increasing cell proliferation e.g by a hormone , both e.g (Through the use of tobacco ) .
The proliferation of normal cells is though to be regulated by growth - promoting oncogenes and counterbalanced by growth constraining tumor suppressor genes .
The development of cancer appears to involve the activation or the altered expression of oncogenes , the loss or inactivation of a tumor suppressor gene , or both .
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