P07.01 18F-fluordesoxyglucose positron emission tomography (FDG-PET) for the detection of the primary lesion in brain metastasis (BM) patients with cancer of unknown primary site (CUPS)

Abstract

Abstract In 30% of patients with brain metastasis (BM), BM are the first clinical manifestation of systemic malignancy, referred to as BM from cancer of unknown primary site (BM-CUPS). The value of F-fluordesoxyglucose positron emission tomography (FDG-PET)/CT in the work-up of BM-CUPS patients remains to be defined. We screened 566 patients operated for BM at the University Hospital Zurich between 2004 and 2014 and identified 127 BM-CUPS patients. Two validation cohorts (n=100 and 120 patients) from independent centers were available. FDG-PET/CT was not superior to CT in localizing the primary lesion as CT (FDG-PET/CT: 73/78, 93.6%; CT: n=70/78, 89.7%; p=0.25, McNemar’s test). Thirty-six of 64 patients (56.3%) showed the same result in spotting the primary tumor and other extracranial lesions. FDG-PET/CT identified additional lesions suspicious for extracranial metastases in 28 patients (43.7%). The graded prognostic assessment (GPA) score was determined post-hoc to objectify clinical relevance of additional findings. Information from CT alone or FDG-PET/CT was used to assess extracranial metastases. Median GPA was 3 for CT vs. 2.5 for PET/CT (p= 3.8x10), resulting in a predicted survival of 5.3 vs. 3.8 months (p= 6.1x10; Wilcoxon’s test). Sensitivity of CT and FDG-PET/CT and staging capabilities were comparable in all cohorts. FDG-PET/CT shows similar sensitivity to detect the primary tumor in BM-CUPS patients as CT, but improves the accuracy of staging. GPA scores and predicted survival differ significantly when calculated based on CT versus FDG-PET/CT. FDG-PET/CT should be prioritized for planning the diagnostic algorithm of BM-CUPS patients and redundant CT imaging should be avoided. Further, randomized trials on BM patients should consider stratification for the respective staging methods when employing GPA scores.