Normal cells divide, grow, die and are replaced in a controlled way. However, when the genetic material of a cell (DNA) becomes damaged, the cell can keep dividing uncontrollably to form a large mass called a tumor.
Tumors can be benign or malignant. A benign tumor is not cancerous, it is localized, grows slowly and usually does not come back when removed.
Malignant tumors are cancerous, they can invade other tissues, and cancer cells can travel via the blood and lymphatic system throughout the body to other organs (metastasize).