Change in bowel habits Constipation, diarrhea, and bowel incontinence, although likely symptoms of numerous other problems, most not serious, can also be a sign of colorectal cancer.

Blood on or in the stool. By far the most alarming of all the symptoms, blood on or in the stool can be a symptom of colorectal cancer. But, it does not necessarily indicate cancer. Numerous other problems can cause bleeding in the digestive tract, including hemorrhoids, ulcers, ulcerative colitis, and Crohn's disease, to name only a few. In addition, iron and some foods, such as beets, can give the stool a red or black appearance, falsely indicating blood in the stool. However, if you notice blood in your stool, see your doctor to rule out a serious condition and to ensure proper treatment is received.