Abstract
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.
Highlights
Cancer of unknown or occult primary (CUP) is defined as the detection of metastatic cancer where the site of primary origin remains obscured even after standardized diagnostic work-up
Out of the 100 patients enrolled with CUP syndrome, 18 patients were excluded from final analysis due to lack of information about their final histopathology results or clinical outcome
Basing conclusions on results from a small group is a limitation to proving efficacy of FDG positron emission tomography-computed tomography (PET-CT) scan in the diagnosis of unknown primary tumor site; the results suggest that incorporation of FDG PET-CT scan in the early diagnostic phase can improve management
Summary
Cancer of unknown or occult primary (CUP) is defined as the detection of metastatic cancer where the site of primary origin remains obscured even after standardized diagnostic work-up. CUPs account for 3 to 5% of all malignancies, and the median age at presentation is 60 years [1,2]. The low rate of primary site detection can be attributed to multiple factors. The median survival in CUP syndrome has been reported as 10-12 months. The prognosis mainly depends on early detection of the primary tumor site coupled with tumor specific therapy. In case of unidentified primary, empiric chemotherapy regimens are offered [5]. Detection of the unknown primary tumor is of crucial importance within this context. Identification of the primary tumor may offer the possibility of a more specific and effective treatment with a consequent improvement in survival
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