Colon with Polyp lateral view
Most cancer in the colon and rectum begins in polyps, tissue masses that grow out of the intestinal wall. Polyps grow slowly and most are benign, but they may become cancerous over time. When a polyp becomes cancerous, it starts to invade the intestinal wall and may spread into nearby lymph nodes or capillaries. From there the cancerous cells can enter into the lymphatic system or the bloodstream and metastasize, spreading to areas distant from the original site. There they may form new tumors.