Not all mutations that lead to cancerous cells result in the
cells reproducing at a faster, more uncontrolled rate. For
example, a mutation may simply cause a cell to keep from
self-destructing. All normal cells have surveillance
mechanisms that look for damage or for problems with their
own control systems. If such problems are found, the cell
destroys itself.
Over time and after many cell divisions, a third mutation
may arise. If the mutation gives the cell some further
advantage, that cell will grow more vigorously than its
predecessors and thus speed up the growth of the tumor.
