Many people with colon cancer have no symptoms at all, until the cancer advances. This makes routine screening for colon cancer and knowing if you are at risk very important.

Many of the symptoms of colon cancer are also symptoms of other diseases of the colon. It is very important to see your doctor if you are having any of the following symptoms, so the proper tests can be run to make a correct diagnosis.

Bleeding: As tumors grow, they can bleed during the passage of feces through the colon. The blood may be visible if the tumor is near the anus however it is more common for blood to be hidden in the stool . Only 20% of people with rectal bleeding have colon cancer, even though it is the most common symptom. Other things, like hemorrhoids can also cause bleeding.

Pain: There are several reasons pain may occur with colon cancer. First, if a tumor grows large enough to block the passageway ( obstruction ), a person can experience pain and swelling of the abdomen. Obstruction can also cause nausea and vomiting if it is severe. Second, if the tumor grows through the wall of the colon into other organs, pain may occur, along with other symptoms, depending on the organ that is affected. Pain can be vague and dull.

Unexpected Weight Loss: Some tumors can cause loss of appetite, leading to weight loss.

Change in Bowel Habits: Colon cancer on the left side can cause constipation, gas pain, painful bowel movements, diarrhea, and narrowing of the stool .