Is an FDG-PET scan the new imaging standard for colon cancer?

In this issue of the Annals of Surgical Oncology, Libutti et al. from the National Cancer Institute (NCI) report the results of a well-designed prospective study that examines the role of the 2-[F] fluoro-2-deoxy-Dglucose (FDG) and positron emission tomography (PET) scan (the FDG-PET scan), carcinoembryonic antigen (CEA) scan, and “blind” second look laparotomy for the detection of recurrent colon cancer in patients with increasing CEA levels.1 They concluded that the FDG-PET scan predicts the patients who will have resectable disease. How does FDG-PET work? The motivation to develop PET came from the understanding that the molecules of organic matter—carbon, oxygen, and nitrogen—can be imaged in their radioactive forms only as positron-emitting isotopes. PET imaging took a leap forward with the use of 2-[F] fluoro-2-deoxy-D-glucose (fluorodeoxyglucose or FDG) which is distributed in the body similar to glucose. The inefficient metabolism of glucose in malignant tumors noted by Warburg 70 years ago allowed detection in vivo of this compound. Because the rate of glycolysis increases proportional to the growth rate of a tumor, FDG-PET imaging potentially provides information regarding the growth rate and tumor grade.2 Does FDG-PET imaging work? The evidence in the literature became so compelling that in 1998 the Health Care Finance Administration and Medicare endorsed PET imaging to differentiate benign pulmonary nodules from non-small lung cancer. In 1999, reimbursement was approved for this imaging modality for the evaluation of lymphoma, melanoma, and recurrent colon cancer.2 Libutti et al. performed an extremely well-designed prospective study to evaluate FDG-PET, CEA scanning, and “blind” second look laparotomy to evaluate colon cancer patients who had both increasing CEA levels and conventional imaging that showed no disease or one site of disease. Of 30 patients who entered the trial, 28 were explored and 26 (94%) had disease discovered. FDGPET found unresectable disease in 9 of 10 (90%) patients who had unresectable disease and resectable disease in 81% of 16 patients who had resectable disease. The CEA scan performed miserably: sensitivity of 18% and specificity of 33%. Interestingly, a “blind” look laparotomy by a second surgeon who was unaware of the results of the FDG-PET and CEA scans was associated with a 92% sensitivity and 100% specificity. This study adds to a growing literature of FDG-PET and CEA scintigraphy in the evaluation of patients with colon cancer. In the 1980’s, CEA scintigraphy seemed promising, but the recent experience suggests the practice has not matched the theory. Investigators in Germany compared FDGPET and CEA scintigraphy by using a CEA Fab’ fragment to evaluate 28 patients with suspected recurrent colorectal cancer.3 Local recurrence was identified in 8 of 9 (88.9%) patients with CEA scintigraphy but metastases were identified in only 1 of 15 (6%) patients. In contrast, FDG-PET correctly identified the local recurrences in all 9 patients and metastases in all 15 patients. Although Libutti et al. appropriately focused their conclusion on the value of FDG-PET, their results regarding the use of the CEA scan—added to those in the literature—suggest that we should put the CEA scan to rest; unless the CEA scan can be improved, it simply should not be used to evaluate patients with suspected recurrent colorectal cancer. FDG-PET previously has been used in patients with increasing CEA levels. Flanagan et al.4 reported on the use of FDG-PET in 22 patients with both abnormal CEA levels and normal conventional imaging studies. Overall, Received August 17, 2001; accepted August 24, 2001. From the University of Massachusetts Memorial Medical Center, Worcester, Massachusetts. Address correspondence to Richard S. Swanson, MD, Chief of Surgical Oncology, University of Massachusetts Memorial Medical Center, University Campus, 55 Lake Avenue North, Worcester, MA 01655; Fax: 508-856-5073; E-mail: swansonr@ummhc.org. Annals of Surgical Oncology, 8(10):752–753 Published by Lippincott Williams & Wilkins © 2001 The Society of Surgical Oncology, Inc.