Colon cancer patients usually experience no symptoms in the early stages of the disease, explains WebMD. Warning signs which appear as the disease progresses include changes in bowel movements, such as frequent constipation or diarrhea, pencil-like stools, abdominal discomfort, bloody stool, and unexplained fatigue.
Because colon cancer shows few symptoms in its early stages, the American Cancer Society recommends regular screening for the disease to ensure it is detected before it progresses beyond the treatable stage. One common test for colon cancer is called a colonoscopy. In this procedure, a doctor inserts a flexible tube containing a camera into the colon and looks for suspicious growths. If a growth is found, it is typically biopsied to determine if it is cancerous.
WebMD recommends that patients who experience bleeding in the rectum or notice blood in the stool speak with a doctor, as these symptoms are not always caused by hemorrhoids. Patients diagnosed with anemia should also discuss the possibility of colon cancer, since bleeding in the digestive tract is one possible cause of anemia. The American Cancer Society notes that while blood in the stool is sometimes an obvious bright red, it can also make the stool simply look darker.