Most colorectal cancers develop slowly over several years. Before a cancer develops, a
growth of tissue or tumor usually begins as a non-cancerous polyp on the inner lining of the
colon or rectum. A tumor is abnormal tissue and can be benign (not cancer) or malignant
(cancer). A polyp is a benign, non-cancerous tumor. Some polyps can change into cancer but
not all do. The chance of changing into a cancer depends upon the kind of polyp: