Cancer is a disease in which certain body cells go out of control and start multiplying rapidly of their own accord. This uncontrolled growth becomes a tumor and eventually will interfere with the working of a vital organ or organs and cause death.

In its early stages, cancer usually has no symptoms, but eventually a malignant will grow large enough to be detected. The following symptoms may signal the presence of some form of cancer.

	A change in the size, color, shape, or thickness of a wart, mole, or mouth sore
	A sore that resists healing
	Persistent cough, hoarseness, or sore throat
	Thickening or lumps in the breasts, testicles, or elsewhere
	A change in bowel or bladder habits
	Any unusual bleeding or discharge
	Chronic indigestion or difficulty swallowing
	Persistent headaches
	Unexplained loss of weight or appetite
	Chronic pain in bones
	Persistent fatigue, nausea, or vomiting
	Persistent low-grade fever, which may be constant or intermittent
	Repeated instances of infection

There are more than 200 forms of cancer, but they all have one thing in common: abnormal cells whose growth is out of control. All cells multiply by splitting in two, a process controlled by genes called oncogenes.

Normally these genes allow just the right amount of cell division to maintain and repair tissue. But changes within a cell can plunge everything out of control, and abnormal cells divide at a very fast rate, doubling over and over. Unlike a benign tumor, as a cancerous tumor grows, its cells gradually invade and destroy neighboring tissues. Cancerous cells may also travel through the bloodstream and lymphatic system to distance parts of the body, there they form secondary tumors.