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PET Scans Following CRC Treatment

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Last Modified: April 23, 2010

Dear OncoLink "Ask The Experts,"

My father (60 year old male, reasonably healthy, diabetic) underwent a colon resection and removed a tumor from the rectosigmoid junction. His cancer is graded Stage IIIB and he got chemotherapy after. His follow up is with CT scans- Is this reliable? Would a PET scan be more sensitive? His doctors have indicated a PET scan is not necessary

James M. Metz, MD, Editor-in-Chief of OncoLink and Assistant Professor of Radiation Oncology at the Hospital of the University of Pennsylvania, responds:

When following a patient after treatment, your fathers’ physicians will use a variety of factors to determine response to therapy. This includes regular history and physical examinations, blood tests, radiologic studies, and colonoscopies. None of these things alone give all the information needed to determine response to treatment. When radiologic studies are ordered, typically CT scans are utilized. This is usually sufficient for most patients and can be very reliable when combined with the other things outlined above. PET scans are not accurate immediately after radiation, surgery, or infectious processes and can be falsely positive. If there is a question of an abnormality on a CT scan, at times a PET scan is ordered in follow up to define the biologic activity. Although PET scans can be sensitive in picking up a cancer, they are not always specific and pick up other things that have nothing to do with cancer. Thus PET scans are not the first choice in following patients after a diagnosis of colon cancer.

This question and answer was part of the OncoLink Brown Bag Chat Series, Colorectal cancer Webchat. View the entire transcript here.