The value of 18F-fluordesoxyglucose positron emission tomography (FDG-PET/CT) in the detection of the primary lesion and for staging in brain metastasis (BM) patients with cancer of unknown primary site (CUPS).

2076 Background: Brain metastasis (BM) are the first clinical presentation of cancer in around 30% of patients. They are then referred as BM from cancer of unknown primary site (BM-CUPS). The value of 18F-fluordesoxyglucose positron emission tomography (FDG-PET)/CT has not yet be determined for the management of these patients. Methods: A total of 566 patients were operated for BM at the University Hospital Zurich between 2004 and 2014, of whom 127 were identified as BM-CUPS patients. Two cohorts from other independent centers (n = 100 and 120) were used for the validation of data. Results: No difference in determining the localization of the primary lesion was observed between FDG-PET/CT and CT (FDG-PET/CT: 73/78, 93.6%; CT: n = 70/78, 89.7%; p = 0.25, McNemar’s test). The same pattern of primary lesion and other extracranial lesions was observed in 36 of 64 patients (56.3%). Additional suspicious extracranial metastases were identified by FDG-PET/CT in 28 patients (43.7%). The median graded prognostic assessment (GPA) scores were 2.5 determined according to FDG-PET/CT and 3 according to CT alone (p = 3.8x10-5), resulting in predicted survival times of 3.8 versus 5.3 months (p = 6.1x10-5; Wilcoxon’s test). Conclusions: A similar sensitivity of FDG-PET/CT and chest CT was observed for the detection of the primary tumor in BM-CUPS, however, FDG-PET/CT significantly improved the accuracy of staging. FDG-PET/CT should be preferred for the management of BM-CUPS and may help to avoid redundant CT imaging.