Cancer is the term for more than 100 different diseases. Cancer is named based on the place in the body where it started. When cancer develops, old or damaged cells survive when they should die, and new cells form when they are not needed. These extra cells can form growths called tumors.

Tumors that are malignant can spread and invade nearby tissues. As tumors grow, some cancer cells can travel to other parts of the body through the blood or lymph system and form new tumors. Benign tumors do not usually return when removed from the body. It is rare to know exactly what causes cancer in someone.