Explain what cancer is, and what the three basic causes are.

Cancerous cells are abnormal cells. Everyone has some of these abnormal cells. Cancer occurs when the genetic program that controls cell growth is disrupted. When this happens, abnormal cells reproduce rapidly and spread to normal tissues and organs. Cancer cells undergo uncontrolled growth for three reasons. Cell mutations may cause cancer genes-known as oncogenes-to undergo abnormal cell division. Other cell mutations may interfere with tumor suppressor genes that keep oncogenes from multiplying. Finally, cell mutations may prevent cells from repairing the DNA errors that occur as a function of cell division, as well as those that occur from exposure to environmental toxins and free radicals.