CMET-26. DIAGNOSTIC VALUE OF FDG-PET/CT FOR PATIENTS WITH BRAIN METASTASIS FROM UNKNOWN PRIMARY SITE

Abstract

OBJECTIVE

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 18F-fluordesoxyglucose positron emission tomography (FDG-PET)/CT in the work-up of BM-CUPS patients remains to be defined.

METHODS

We screened 566 patients operated for BM at the University Hospital Zurich between 2004 and 2014 and identified 127 BM-CUPS patients. A validation cohort from two independent centers (n=100 and 120 patients) was available.

RESULTS

FDG-PET/CT was not superior to CT in localizing the primary lesion (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. 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 only or FDG-PET/CT was used to assess extracranial metastases. Median GPA was 3 for CT vs. 2.5 for PET/CT (p= 3.8x10-5, McNemar's test), resulting in a predicted survival of 5.3 vs. 3.8 months (p= 6.1x10-5; Wilcoxon's test). Sensitivity of CT and FDG-PET/CT and staging capabilities were comparable in all cohorts.

CONCLUSION

FDG-PET/CT shows similar sensitivity to detect the primary tumor in BM-CUPS patients as CT, but may improve the accuracy of staging by detecting of more metastases. 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 standardize the methods when stratifying for GPA.