The mass of extra cells forms a growth or tumor. Tumors can be benign or malignant. Benign tumors are not cancerous. They often can be removed and, in most cases, they do not come back. Cells in benign tumors do not spread to other parts of the body, and they are not life threatening.
Malignant tumors are cancerous.
Cells in malignant tumors are abnormal and divide without control or order. These cancer cells can invade and destroy the tissue around them. Cancer cells also can break away from a malignant tumor and enter the bloodstream or lymphatic system vessels. This process, called metastasis, is how cancer spreads from the original tumor to form new tumors in other parts of the body. See our privacy policy , terms of use , ad rates and legal notices .