Diagnostic and prognostic value of F-18 FDG PET/CT in patients with carcinoma of unknown primary

OBJECTIVE: Carcinoma of unknown primary (CUP) is inability to detect primary tumor despite all imaging methods with a biopsy-proven tumor metastasis. In the present study, we aimed to investigate the diagnostic and prognostic value of F-18 fluorodeoxyglucose (F-18 FDG) positron emission tomography/computed tomography (PET/CT) in patients with CUP. METHODS: The patients with a diagnosis of CUP between November 2009 and January 2020 were evaluated retrospectively. A total of 155 patients (96 men and 59 women) were included in the study. Survival rates of the patients were evaluated by Kaplan–Meier and log-rank statistical analysis. RESULTS: The correctly determined primary tumor by F-18 FDG PET/CT was found in 64 patients (41%) (true positive). F-18 FDG PET CT results were negative (false negative) in determining primary tumor localization in 14 (9%) patients whose had local disease. Of the 155 patients, 66 (42.5%) had true-negative results and 11 (7%) had false-positive results. The sensitivity of 82%, specificity of 86%, and accuracy of 84% were calculated. The SUV(max) value of the malignant lesion was on average 8.9 (range 3.6–26.1). Kaplan–Meier analysis revealed that the 1-year survival rates were 37.3% in regional disease and 16% in extensive disease (log-rank test, p=0.021). CONCLUSION: F-18 FDG PET/CT is a useful method in the detection of primary tumor in patients with CUP. F-18 FDG PET/CT can be helpful the evaluation of the prognosis by showing the extent of the disease.