Colon cancer may not produce symptoms until it's quite advanced. It's usually painless and develops deep in the abdomen, where it enlarges over time. Microscopic blood loss or gross bleeding may herald the existence of colon cancer. If the tumor becomes large enough to block the intestine or place pressure on adjacent organs, pain and/or a change in bowel movements may result.
Blood Loss
The Merck Manuals Online Medical Library says blood loss, or symptoms related to blood loss, are sometimes the only symptoms of colon cancer. Most tumors bleed at some point, but often the bleeding is not visible to the naked eye and may go unnoticed. Visible blood in or around the stool should be evaluated. The anemia that results from this blood loss may bring about pale skin, shortness of breath, an increased heart rate and profound fatigue and weakness.
Change In Bowel Habits
A malignant tumor in the colon may become large enough to alter the size, shape or consistency of the stool. Some cancers, especially if located in the left side of the colon, encircle the diameter of the bowel and make the stool smaller. The bowel movement may appear ribbon or pencil-shaped. As the tumor enlarges, feces may not progress normally, absorb more water and pass as a more liquid stool. This may produce a pattern of alternating constipation and diarrhea, as described by the American Cancer Society. Difficulty moving the bowels may result in a feeling of incomplete rectal emptying after a bowel movement. Alternatively, the presence of the tumor itself may produce the same symptom.
Pain
Pain tends to be a late symptom in colon cancer sufferers nearing the end of life. Pain during a bowel movement is described by the University of Maryland Medical Center. This may be related to the narrowing of the bowel passageway by the tumor. This same mechanism may produce stomach or intestinal cramps. Pain in the abdomen may also result from invasion of the tumor on adjacent structures, or simply from pressure.
Weight Loss
Unexplained or unintended weight loss may be seen in late-stage colon cancer patients, as noted by the National Cancer Institute. This may be secondary to the alteration in appetite and digestion from the tumor. In addition, the metabolic demands on the body increase due to the stresses of fighting a severe illness, and keeping up with caloric needs becomes a challenge.
