Rectal cancer is a disease in which malignant (cancer) cells form in the tissues of the rectum. Health history affects the risk of developing rectal cancer. Signs of rectal cancer include a change in bowel habits or blood in the stool.Cancer of the rectum should be considered whenever there is rectal bleeding, even if other causes such as hemorrhoids are present. A person may feel as if there is incomplete evacuation. There usually is no pain until later stages of the condition.Rectal cancer occurs when cells in the rectum mutate and grow out of control. The disease may also develop when growths, called polyps, on the inner wall of the rectum develop and become cancerous. The risk of rectal cancer increases with age. The average age of a person diagnosed with colorectal cancer is 68.