A Systematic Review of the Efficacy of 18F-FDG PET in Unknown Primary Tumors

Patients with unknown primary tumors (UPT) represent a challenge for clinicians, as management decisions depend on the localization of the primary tumor and accurate staging. In this article we systematically reviewed the evidence on the efficacy of 18F-FDG PET in patients with UPT, analyzing the diagnostic performance, impact on management and patient outcome efficacy. The performance of 18F-FDG PET in primary tumor detection was high, as it detected the primary tumor in >40% of patients with high sensitivity and intermediate-high specificity. Most cases in which no primary tumor was found remained true-negative after follow-up. Moreover, most studies included patients with negative conventional imaging methods. Studies presented variable results regarding changes in management, reporting a high impact on management in 44% of patients in the pooled data (range 14%-69%). However, this variability could be due to differences in study design. Patient outcome efficacy was discussed by several studies, with conflicting and inconclusive results. Future studies must supply high quality evidence regarding impact on management, patient outcome efficacy, and cost-effectiveness issues; additionally, the role of PET/CT must be evaluated. In our opinion, 18F-FDG PET should be performed at the onset of the diagnostic work-up; this may improve management decisions and patient outcome.