Diagnostic Value of 18F-FDG PET/CT in Patients with Carcinoma of Unknown Primary

The aim of this study is to investigate the clinical role of 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) in patients with carcinoma of unknown primary (CUP).Methods: One hundred twenty one patients with a diagnosis of CUP who underwent whole body 18F-FDG PET/CT imaging were included in this retrospective study. The final diagnoses were confirmed either histopathologically or by clinical follow-up. Results: The 18F-FDG-PET/CT successfully detected the primary tumor in 59 out of 121 (49%) patients. The most common primary tumor as detected by 18F-FDG PET/CT was lung cancer (n=31). In a patient, two primary tumors (colon and prostate) were detected on PET/CT imaging. Bone marrow biopsy revealed prostate cancer in this patient and the colon cancer was accepted as a synchronous second primary tumor. 18F-FDG PET/CT findings were false-positive in 11 patients. 18F-FDG PET/CT could not detect any primary lesion in 51 patients, whose conventional work-up detected a primary tumor in 11 and thus considered as false-negative. The sensitivity, specificity rate and accuracy of 18F-FDG PET/CT in detection of primary tumor were identified as 84%, 78% and 82%, respectively.Conclusion: Whole body 18F-FDG PET/CT is an effective method for detecting the primary tumor in patients with CUP. In addition to detecting the primary tumor, it can also help determine disease extent and contribute to patient management.