Tumors of the colon and rectum are growths (masses) arising from the wall of the large intestine. Benign tumors of the large intestine are usually called polypoid in shape. Malignant tumors of the large intestine are called cancers, and most are believed to have developed from polyps. Bleeding from colon polyps and cancers tends to be mild (the amount of blood loss is small), intermittent, and usually does not cause low blood pressure or shock.
Cancers and polyps of the colon and rectum can cause bright red rectal bleeding, maroon colored stools, and sometimes melena. The colon cancers and polyps located near the rectum and the sigmoid colon are more likely to cause mild intermittent bright red rectal bleeding; while colon cancers located in the right colon are more likely to cause occult bleeding that over time can lead to moderate or severe iron deficiency anemia.
Colon polyps found during colonoscopy usually are removed, a process called polypectomy. Bleeding can