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Cancer occurs
when cell division gets out of control. Usually, the timing of cell division
is under strict constraint, involving a network of signals that work together
to say when a cell can divide, how often it should happen and how errors
can be fixed. Mutations in one or more of the nodes in this network can
trigger cancer, be it through exposure to some environmental factor (e.g.
tobacco smoke) or because of a genetic predisposition, or both. Usually,
several cancer-promoting factors have to add up before a person will develop
a malignant growth with some exceptions.
The predominant mechanisms for the cancers featured
are:
- Impairment
of a DNA repair pathway
- The transformation
of a normal gene into an oncogene and
- The malfunction
of a tumor supressor gene
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