Sometimes anal cancer causes no symptoms at all. But bleeding is often the first sign of the disease. The bleeding is usually minor. At first, most people assume the bleeding is caused by hemorrhoids painful, swollen veins in the anus and rectum that may photos of anal cancer. They are a benign and fairly common cause of rectal bleeding. Most often these types of symptoms are more likely to be caused by benign non-cancer conditions, like hemorrhoids, anal fissures, or anal warts.