18F-fluorodeoxyglucose positron emission tomography (18FDG-PET) for patients with biliary tract cancer: systematic review and meta-analysis.

INTRODUCTION: The role of 18 F-fluorodeoxyglucose positron emission tomography (18 FDG-PET) in the diagnosis and staging of patients with biliary tract cancer (BTCs) remains controversial.

METHODS: This systematic-review and meta-analysis explored the diagnostic test accuracy (DTA) of 18 FDG-PET as a diagnostic tool for diagnosis of primary tumour (T), lymph node (N), distant metastases (M) and relapsed disease (Rel). Subgroup analysis by study quality and BTC subtype were performed. Changes in management based on 18 FDG-PET and impact of maximum standardized uptake values (SUVmax) on prognosis were also assessed. Random effects model was used for meta-analyses (MataDiSc v.1.4; Stata v.12; RevMan v.5; R-Studio v.8.1).

RESULTS: Of 47 eligible studies, 2,125 patients were included. Pooled sensitivity (Se) and specificity (Sp) for patients with BTC were: T [Se 91.7% (95% CI 89.8-93.2); Sp 51.3% (95% CI 46.4-56.2); area under the curve (AUC) 0.8668]; N [Se 88.4% (95% CI 82.6-92.8); Sp 69.1%(95% CI 63.8-74.1); AUC 0.8519]; M [Se 85.4% (95% CI 79.5-90.2); Sp 89.7%(95% CI 86.0-92.7); AUC 0.9253]; Rel [Se 90.1% (95% CI 84.4-94.3); Sp 83.5%(95% CI 74.4-90.4); AUC 0.9592]. No threshold effect was identified. Meta-regression did not identify significant sources of heterogeneity. Sensitivity analysis did not reveal changes in results when analyses were limited to studies with low risk of bias/concern (high quality). Pooled proportion of change in management was 15% (95% CI 11-20); majority (78%) due to disease upstaging. Baseline high SUVmax was associated with worse survival (pooled HR of 1.79 (95% CI 1.37-2.33); p-value <0.001).

CONCLUSIONS: There is evidence to support the incorporation of 18 FDG-PET to the current standard of care staging imaging/diagnostic tests performed for the assessment of N, M and Rel to guide adequate treatment selection; especially if the identification of occult sites of disease would change management (i.e. surgery/local therapies) or if diagnosis of Rel remains unclear following standard of care imaging. The use of 18 FDG-PET for diagnosis of primary tumour (T) in the absence of other disease sites or pathological confirmation remains controversial, due to low specificity.

LAY SUMMARY: A positron emission tomography (PET scan), using 18F-fluorodeoxyglucose (18FDG), can help doctors identify areas of cancer in the body by highlighting "hot spots". These hotspots may be cancerous (true positive) but may also be non-cancerous, like inflammation (false positive). In this study all the published research of PET scans in patients with biliary tract cancer has been reviewed (systematic analysis) and the available information studied together (meta-analysis). We show that PET scans are useful to assess how far advanced the cancer is (by assessing spread to lymph glands and to other organs); and also useful to identify if the cancer has recurred (for example after surgery), thus helping doctors to make treatment decisions. However, it is not useful to first diagnose a biliary tract cancer due to the high chances of a "false positive" (diagnosing a cancer when there isn't one). Therefore, doctors should not rely on 18FDG-PET for diagnosis; a biopsy is still necessary.