Predisposing factors include chronic ulcerative colitis, granulomatous colitis, and familial polyposis. Populations with a high incidence of colorectal cancer eat diets low in fiber and high in animal protein, fat, and refined carbohydrates. Although carcinogens may be ingested in the diet, it seems more likely that they are produced from dietary substances or from biliary or intestinal secrtions, probably by bacterial action. The exact mechanism is unknown. Symptoms, Signs and Diagnosis Adenocarcinoma of the colon and rectum grows slowly and a long interval elapses before it is large enough to produce symptoms.
Early diagnosis depends on routine examination.
Bleeding is usually occult. Fatigue and weakness due to severe anemia may be the only complaint. Partial obstruction with colicky abdominal pain or complete obstruction may be the presenting picture. The stool may be streaked or mixed with blood. In cancer of the rectum the most common presenting symptom is bleeding with defecation.