Cancer is not caused by an overproduction of cells.
Normal cells live only so long and then die.
Cancer cells live forever and become so numerous that they invade other tissues. Cancer cells eventually invade and kill normal cells that are necessary for life and the victim dies. For example, if you have cancer of the kidney, the kidney cells can become so numerous that they invade and grow in your lungs. This prevents your lungs from processing oxygen and you smother to death. The kidney cancer cells could invade your bones and cause them to break.