18F-FDG PET-CT in Unknown-Source of Elevated Serum Carcinoembryonic Antigen (CEA) Level.

Objective: To investigate the clinical value of 18F-FDG PET-CT in the diagnosis of malignant tumor when serum carcinoembryonic antigen (CEA) level is elevated for unknown primary lesion.

Study Design: A descriptive study.

Place And Duration Of Study: Department of Nuclear Medicine, Luoyang Central Hospital Affiliated to Zhengzhou University, Henan, China, from March 2015 to March 2017.

Methodology: A total of 120 cases of parallel 18F-FDG PET-CT examination with serum CEA level of patients with unexplained source examined were chosen. Those with a known disease or with incomplete record of clinical and/or relevant laboratory examinations were excluded. Pathological examination, results of clinical follow-up and other imaging tests constituted the clinical value of 18F-FDG PET-CT in the diagnosis of tumor. For patients who had underwent the determination of serum CEA more than twice, CEA doubling time (DT) was also calculated. The serum CEA level and CEA DT of benign versus malignant 18F-FDG PET-CT imaging results were compared.

Results: Thirty (25.00%) cases were finally diagnosed as malignant tumors, and 90 (75.00%) cases were excluded labelled benign condition. There was one false positive case and one false negative case each with 18F-FDG PET-CT diagnosis. The sensitivity, specificity, accuracy, positive predictive value and negative predictive value were 96.7%, 98.9%, 98.3%, 96.7% and 98.9%, respectively. The serum CEA level of patients with positive 18F-FDG PET-CT imaging was higher than that of 18F-FDG PET-CT negative patients (p<0.001). The serum CEA DT of patients with positive 18F-FDG PET-CT imaging was shorter than that of 18F-FDG PET-CT negative patients (p<0.001). The receiver operating characteristic (ROC) curve analysis showed that the diagnostic efficacy of 18F-FDG PET-CT was best at serum CEA of 14.31 μg/L.

Conclusion: 18F-FDG PET-CT imaging has high diagnostic value for patients with elevated serum CEA. For patients with serum CEA over 14.31 μg/L, the diagnostic value of 18F-FDG PET-CT for malignant tumors is more reliable.