Purpose: Serum carcinoembryonic antigen elevation without detectable relapse during colorectal cancer follow-up presents a challenge. This study was designed to evaluate the utility of fluorine-18-labeled 2-fluoro-2-deoxy-D-glucose positron emission tomography in colorectal cancer patients with unexplained carcinoembryonic antigen elevation at different levels.
Methods: Thirty-seven colorectal cancer patients referred for positron emission tomography after primary surgery who had serum carcinoembryonic antigen levels >5 ng/ml and negative or equivocal conventional imaging studies were analyzed. Patient status was determined by histopathology and/or clinical follow-up. Grouping as disease-free, potentially resectable, or advanced disease was performed. The management impact was defined as the percentage of patients with a true-positive positron emission tomography result.
Results: The sensitivity, specificity, and accuracy of positron emission tomography for relapse detection were 89, 89, and 89 percent, respectively. The management impact was 68 percent. In 24 patients with carcinoembryonic antigen levels <25 ng/ml, positron emission tomography helped correct patient grouping in 20 patients (83 percent), including 8 in the disease-free group, 5 in the potentially resectable group, and 7 in the advanced-disease group. In 13 patients with carcinoembryonic antigen levels >25 ng/ml, positron emission tomography identified 8 patients in the advanced-disease group and 1 patient in the potentially resectable group but missed 2 patients with relapse and undergrouped 2 patients in the advanced-disease group as potentially resectable.
Conclusions: 2-fluoro-2-deoxy-D-glucose positron emission tomography can help triage patients for appropriate management with unexplained carcinoembryonic antigen elevation <25 ng/ml. For patients with unexplained elevation of carcinoembryonic antigen >25 ng/ml, the utility of positron emission tomography is mainly to confirm the presence of advanced disease and occasionally to identify potentially resectable lesions.