Diagnostic Accuracy of 18F-Fluorodeoxyglucose Positron Emission Tomography-Computed Tomography in the Evaluation of Carcinoma of Unknown Primary

OBJECTIVE Detection of primary tumor site in patients with carcinoma of unknown primary (CUP) syndrome has always been a diagnostic dilemma, necessitating extensive workup. Early detection of primary tumor site coupled with specific therapy improves prognosis. The low detection rate of the primary tumor site can be attributed to the biological behavior or the small size of the primary tumor to be detected by conventional imaging. The objective of this study was to evaluate the diagnostic accuracy of 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET-CT) in detecting CUP. METHODS A retrospective, cross-sectional analysis of 100 PET-CT scans of patients with CUP syndrome between November 2009 and December 2013 was performed. Eighteen patients whose final histopathology results could not be obtained for correlation were excluded from analysis. The hypermetabolic sites were assessed in correlation with histopathology. The diagnostic accuracy, sensitivity, specificity, positive predictive value and negative predictive values were assessed for PET-CT. RESULTS Out of the 82 patients, primary tumor was correctly identified in 57.3% patients by 18F-FDG PET-CT (true positive). The PET-CT scan results were negative for primary site localization in 15% of patients (false negative). While 21% had true negative results, 7.3% displayed false positive results. PET-CT scan upstaged the disease in 27% cases. Overall, the diagnostic accuracy was found to be 78%, sensitivity 80%, specificity 74%, positive predictive value 88.7% and negative predictive value 59%. CONCLUSION Our data supports the utility of 18F-FDG PET-CT scan in the localization and staging of CUP syndrome.