Early detection of colorectal cancer through screening is essential. Even individuals without symptoms should be screened on a regular basis. Symptoms may include:

• feeling tired and weak;
• jaundice (a yellowish coloration of the skin);
• pain or cramps in the abdomen;
• differences in the patient's usual bowel habits: constipation, diarrhea, narrowing of stool;
• feeling of fullness in bowel that is not relieved by a bowel movement;
• bleeding from rectum;
• blood in stool; and
• reduced appetite.

The patient may not even notice the gradual onset of some of these relatively nonspecific symptoms. The doctor may interpret them as being caused by something else.

When cancer is more advanced, the bowel may become perforated. This can cause a serious abdominal illness. The cancer may even have spread to other organs. Shortness of breath or liver dysfunction may be the first noticeable symptoms.