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e've known for a long time that cancer cells, unlike
normal cells, multiply uncontrollably, ignoring the usual signals to stop.
We also know that cancer cells can metastasize -- migrate from their original
site and set up shop in another part of the body, where they continue to
multiply unchecked.
But over the past two decades cancer research has uncovered much more. We now know that all neoplastic transformations (cancers) result from mutations, or changes, in genes that control cell growth and behavior. These genes normally restrict cell proliferation and direct the cell to repair DNA damage, or failing that, to self-destruct, a process called apoptosis, or cell 'suicide.' The mutated genes free the cell from these controls, allowing it to divide continuously and to pass on the mutation(s) to its progeny.
What causes these mutations? Many factors come together to cause each
type of cancer. Genetic mistakes can be inherited or they can be acquired
as a result of exposure to chemicals, radiation, or viruses. Random mistakes
also occur each day in the course of duplicating the three billion units
in our DNA during cell division. No one mutation is enough to make a cell
cancerous. Multiple genetic changes, in specific classes of genes, are needed
to transform a normal cell into a neoplastic cell that grows out of control.
A small percentage of people inherit a susceptibility for certain types
of cancer, putting all their body's cells one step closer to the disease.