Original Article18F-FDG PET/CT superior to serum CEA in detection of colorectal cancer and its recurrence☆
Introduction
Since its introduction in 1965, serum carcinoembryonic antigen (CEA) has been an important tumor marker in the management of colorectal cancer (CRC) [1]. CEA does not play a significant role in the staging of CRC due to its low sensitivity [2]; however, serial CEA measurements are recommended by both the 2008 National Comprehensive Cancer Network (NCCN) practice guidelines as well as the 2005 American Society of Clinical Oncology (ASCO) guidelines for the surveillance for CRC recurrence [3].
Positron emission tomography (PET)/computed tomography (CT) is a hybrid imaging modality that takes advantage of the high rate of glycolysis in malignant tumor cells (PET), as well as precise anatomic correlation (CT). PET/CT has not been studied extensively in the initial staging of CRC mainly due to low reported sensitivity in detecting local lymph node involvement [4]. But recently, PET/CT has been reported to have a very high sensitivity and specificity in the detection of CRC recurrence. In a study of 68 patients with CRC recurrence, Chen reported a sensitivity of 94.6% and specificity of 83.3% with PET/CT [5]. Similar results were reported by Cohade [6].
The 2008 NCCN practice guidelines for colorectal cancer suggest performing a PET scan only in the context of an elevated serum CEA. However, to our knowledge, a direct comparison between PET/CT results and serum CEA has not been done to justify this recommendation. The objective of this paper is to determine if PET/CT can detect more CRC recurrences than elevated serum CEA levels would suggest, and whether a revision of current guidelines for surveillance of CRC recurrence is needed.
Section snippets
Study design and patient population
A retrospective review of 639 patients referred for 18F-FDG PET/CT imaging to the McGill University Health Centre between September 2005 and October 2007 for initial staging of CRC or surveillance of CRC recurrence was performed. Of the 639 patients imaged, 328 had corresponding serum CEA measurements done within 4 months of the PET/CT scan. These were subsequently categorized into two groups: the initial staging group had 189 patients, and the surveillance of CRC recurrence group had 139
Results
From the 189 patients referred for initial staging of CRC, PET/CT detected approximately 2.5 times (n= 182) as many CRCs as CEA (n= 73) (Table 1). All 182 PET/CT-positive cases had histologically proven CRC. Seven patients had both negative PET/CT and CEA, and subsequent workup did not reveal any evidence of CRC in these patients.
From the 139 patients referred for surveillance of CRC recurrence, PET/CT detected approximately 1.5 times (n= 99) as many CRC recurrences as CEA (n= 65). All 99 PET/CT
PET/CT as initial diagnostic staging modality
Serum CEA has a very low sensitivity in the diagnostic workup of CRCs. In a recent study of 425 CRC patients, only 42.6% of all diagnosed CRC patients had an elevated preoperative CEA [2]. In our series, PET/CT detected 2.5 times as many CRC at initial staging as serum CEA (Fig. 1). These findings suggest that despite the shortcomings of its predecessor (PET), PET/CT's role in the initial staging of CRC warrants closer examination.
PET/CT in detection of CRC recurrence and metastases
Recurrence of CRC occurs in about one third of patients within
Conclusion
PET/CT is far superior to serum CEA for detecting CRC, both preoperatively and during surveillance of disease recurrence. PET/CT detects 2.5 times as many CRCs at initial staging and 1.5 times as many CRC recurrences as serum CEA. Elevated serum CEA levels cannot be relied upon by the clinician to raise the suspicion of disease recurrence. More than a third of all CRC recurrences are CEA negative (even with serial CEA measurements) but detectable by PET/CT. Our results suggest that PET/CT
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This manuscript or any figure or table in it has not been submitted to any publication previously. None of the authors have any financial or other relationships that might lead to a conflict of interest. The manuscript has been read and approved by all the authors, and the requirements for authorship have been met. Each author believes that the manuscript represents honest work.