A diagnosis of cancer marks an abrupt change in the life of the patient. A line of demarcation has been drawn.
Life seems to be separated into before and after.
Yet the events that lead a cell to become cancerous take place gradually, sometimes over periods that can exceed 10 years. During this lengthy evolution, cells undergoing cancerous transformation accumulate genetic abnormalities, one important consequence of which is that cellular growth becomes deregulated. The number of cells in normal tissue is strictly controlled by a system of checks and balances. Cells that are too old, that fail to function properly or that are otherwise no longer needed are programmed to die, a process known as apoptosis . These cells are replaced by new cells, derived from primitive precursors, also called stem cells , that divide and then differentiate into the mature cell type that performs a specific function.