The genetically altered cells have, over time, reproduced
unchecked, crowding out the surrounding normal cells. After
a period of ten years, the growth may contain one million
cells and be the size of a pinhead. At this point the cells
continue to look the same as the surrounding healthy cells.
After about a million divisions, there's a good chance that
one of the new cells will have mutated further. This cell,
now carrying two mutant genes, could have an altered
appearance and be even more prone to reproduce unchecked.
