Colon Cancer Early Symptoms. Unfortunately, in most cases of colon cancer, early symptoms do not occur. Signs and symptoms generally develop only after the disease has spread beyond its earliest, most treatable stages. Once symptoms do appear, they may include blood in the stool, abdominal discomfort, and change in frequency of bowel movements. For most people with colon cancer, early symptoms do not develop. So it's important to have regular screening tests to check for colon cancer, even when no symptoms are present. In the later stages of colon cancer, symptoms are more common. These symptoms of colon cancer may include: 1  A change in the frequency of bowel movements. 2  Diarrhea, constipation, or feeling that the bowel does not empty completely.  Either bright red or very dark blood in the stool.