A benign tumor is not cancer, does not spread, can usually be completely removed, is not likely to recur and does not usually present a serious threat to health.
A malignant tumor is cancer, and can invade neighbouring tissue and organs through blood or lymph system (this is the system which helps fight infection). This is called metastasis and can start new or secondary cancers.
The cells in almost any part of the body can become cancerous (only the hair, nails and teeth cannot get cancer). There are several hundred different types of cancer. Each happens for different reasons and each type of cancer is different. Some cancers develop slowly, others quickly, some cancers have known causes whilst others have unknown causes. When cancer comes back in a person who appeared to be free of the diseases after treatment, it is called a recurrence.