What is Cancer?
A tumor can be benign - harmless - or malignant - bad. Benign tissues are rarely a threat to life, unless in a major organ. These do not invade the surrounding tissue and do not spread. They can usually be removed and do not come back. But malignant tumors grow into the surrounding tissue in a process called invasion. Cancer cells also break away from a malignant tumor and enter the blood stream or lymphatic system. This is how cancer spreads from the original tumor to other tissues and organs. The spread of cancer is called metastasis.