While colon cancer may be asymptomatic in its early stages, tumor growth can cause changes in bowel habits. Someone who never had a problem with diarrhea may develop persistent diarrhea that does not clear up within a few days. Diarrhea that does not go away should be reported to a physician for evaluation.

Persistent Vomiting

The growth of a tumor in the colon can cause nausea and vomiting. This is because the tumor can cause pressure on the abdominal organs. Vomiting that does not go away after a few days should be evaluated by a medical professional. Diagnostic tests, such as a CT scan or x-ray, may be used to determine if a tumor is present.

Cramping Abdominal Pain

The pressure of a tumor growing in the intestine can cause cramping abdominal pain. Because abdominal pain can accompany a number of other conditions, it should be evaluated by a physician if it continues over a long period of time. Laboratory or diagnostic tests may be used to determine the cause of persistent abdominal pain.

Persistent Bloating

As a tumor grows in size, it can cause persistent bloating. Someone with colon cancer may notice that the abdomen is bloated and rigid instead of soft. Bloating is also associated with premenstrual syndrome, intestinal gas and other conditions, so it needs to be evaluated to determine the cause.

Unexplained Weight Loss

Colon cancer can be signaled by unexplained weight loss. When someone with colon cancer does not feel well, he may decrease his daily food intake. The body continues to use the same amount of calories as usual, creating a calorie deficit. This causes unintended weight loss.

Decreased Stool Size

As digested food moves through intestines, it is shaped into stool. Tumors growing in the colon can make the intestines narrower, which leaves less room for digested food to move. This makes the stools narrower. Pencil-thin stools can be a cause for concern and should be reported to a medical professional.

Unexplained Fatigue

Unexplained fatigue is associated with most types of cancer. While the exact causes of this fatigue are not known, physicians from the Mayo Clinic indicate that there are several things which can contribute to this fatigue. Some cancers release chemicals called cytokines, which are thought to cause fatigue. If the cancer destroys healthy red blood cells, someone with colon cancer can develop anemia. Anemia causes fatigue.