Symptoms and Complications
Polyps and colon cancer usually cause slow, steady bleeding in the colon. The blood emerges with the stool, but is often invisible. Many other conditions can cause blood in the stool, but if you experience it you should consult a doctor. Often, the blood loss isn't seen, but its effect is felt as iron-deficiency anemia. Men and postmenopausal women with symptoms of anemia need a checkup.
Cancer in the upper part of the colon often causes no symptoms. Cancer in the lower part may cause obstruction and constipation. More often, colon cancer has none of these symptoms until the disease is advanced. That's why screening is so vital.