Colon Cancer and PET/CT

Colorectal cancer affects 1 person in 20 in the US and Europe. The ACS estimates that 107,300 new cases of colon cancer and 41,000 new cases of rectal cancer in the United States in 2002. Colorectal cancer will be responsible for about 56,600 deaths in 2002.

The good news is that the death rate from colorectal cancer has been going down for the past 20 years. This may be because more of the cases are found early, and also because treatments have improved. About 70% of patients diagnosed with colorectal cancer will undergo surgery although one-third of these patients will develop recurrence some time after surgery.

As with all types of cancer, early diagnosis of colorectal cancer is key to its cure. Colorectal cancers probably develop slowly over a period of several years. Before a true cancer develops, there are often earlier changes in the lining of the colon or rectum. If found early, before it has metastasized, the disease is considered curable. However, as the tumor spreads to lymph nodes, a patient's chance of living at least five years drops to 40 - 60%. If the cancer has already spread to distant organs, the long-term survival is much lower.

Before PET, it was extremely difficult to monitor for suspected recurrence. The other techniques available for staging and assessment of potential recurrences lack sensitivity and precision and frequently result in diagnostic and therapeutic delays. In many colorectal patients, pelvic CT will demonstrate a suspicious mass, but cannot distinguish mass tumor recurrence from postoperative or postradiation scar. Further evaluation usually involves a biopsy. A positive biopsy is highly predictive of recurrence but because it is impossible to sample the entire mass, a negative biopsy cannot exclude recurrence.

Follow up

For several years after treatment, it is important to have regular follow-ups to find out if any active cancer cells return. Physical and rectal exams by a physician, regular colonoscopy, and blood tests are important to help tell if the cancer has come back. Blood markers like CEA are present in some patients with active colon cancer, so a rise in these blood values is used as an early warning sign that the cancer has returned. But some people without cancer also have CEA in their blood, so it cannot be a specific test for cancer.

Imaging with PET is also critical in looking for the return of the cancer. Before PET, it was extremely difficult to monitor patients for the recurrence of cancer. Earlier imaging tests might not see the cancer as sensitively as PET, which could result in a delay of further treatment. In many patients with colorectal cancer, a mass may develop in the pelvis. This mass can be seen on a CT scan, but CT cannot determine whether the mass resulted from surgical or radiation scarring, or is a recurrent cancer that must be treated.

A PET scan can identify whether the mass is cancerous because it will pick up the radioactive glucose and be seen on the scan results. If, however, the mass is scarring caused by the radiation treatments, no glucose uptake will be seen in the area of the mass.

PET can be used to image tumor response to therapy and to detect recurrence in successfully treated lesions. After surgery and other treatments, PET is an extremely important tool in monitoring whether any cancer cells have returned and if treatment should be re-started.

Colorectal cancer rarely recurs after 5 years; thus most patients who live 5 years without recurrence are considered cured. In the interim, however, make sure that PET is a part of your regular testing.

How Does PET/CT Make a Difference

Whole-Body PET imaging is the most accurate diagnostic test for detection of recurrent colorectal cancer, and is a cost-effective way to differentiate resectable from non-resectable disease. A PET scan is indicated whenever a major management decision depends upon accurate evaluation of tumor presence and extent.

More Information

Find the support you need! If you've had a colostomy, follow-up is an important concern. You may feel worried or isolated from normal activities. Whether the colostomy is temporary or permanent, there are health care professionals trained to help you. And, there are programs offering information and support. The stress of any illness can often be helped by joining a support group where members share common experiences and problems.

Information is available from the following groups:

Academy of Molecular Imaging's World of PET
American Cancer Society
National Colorectal Cancer Research Alliance
International Association for the Study of Lung Cancer
Medline Plus Colorectal Cancer
National Cancer Institute