Colon Cancer

Diagnosis

A polyp as seen during a colonoscopy.

When polyps and early-stage cancers are found and removed, the cure rate approaches 100 percent. That is why appropriate screenings of those at risk for polyps (see risk factors) and accurate diagnostic procedures are so important. Below are listed the main diagnostic procedures used at Mayo Clinic. If cancer is found, some of these tools also help doctors determine the stage (extent) of the disease. This information is used to develop a treatment plan.

• Flexible sigmoidoscopy: A flexible, slender, lighted tube with a tiny camera is used to examine the rectum and the sigmoid. The sigmoid is the last 2 feet of the colon. Nearly half of all colon cancers occur in this area.
• Barium enema: This test allows the doctor to evaluate the entire large intestine with an X-ray. Barium, a contrast dye, fills and coats the lining of the bowel, creating a clear silhouette of the rectum, colon and sometimes a small portion of the small intestine. The colon appears white; growths show up as dark areas.
• Colonoscopy: This technique allows the doctor to directly view the entire colon with a thin, lighted, flexible tube called an endoscope. The endoscope contains a tiny camera. Small polyps may be removed during an exam. Colonoscopy is the best diagnostic tool currently available for colon cancer. Some patients find the necessary bowel preparation inconvenient and uncomfortable. The examination also may include some discomfort, and patients may be given a mild sedative. The exam takes about 30 minutes.
• Endoscopic ultrasound: Very high-frequency sound waves are used to produce images of the colon. The advantages of this procedure are that it is safe and minimizes discomfort. An ultrasound probe is added to an endoscope to obtain the images. The endoscope also contains cutting tools that can take tissue samples of the main cancer or surrounding lymph nodes for analysis in the lab.
• PET scan: Positron Emission Tomography is a noninvasive diagnostic tool that takes a different approach than other imaging technologies. Instead of providing a clear picture of the physical structure of organs and tissues, PET scans provide information about chemical activity within the organs and tissues. As a result, they may reveal relapse at the site of the main tumor or cancer elsewhere in the body earlier than other imaging techniques. A PET scan also may be better than other imaging techniques at distinguishing between malignant and benign growths.
• CT colonography: Mayo Clinic has been involved in research of this technique since its inception and has performed more CT colonographies than any other institution. Currently, doctors at Mayo Clinic perform about 1,000 such examinations per year.