Accuracy of 18F-FDG PET in Early Metastatic Testicular Seminoma: Analysis from the SEMS Trial.

Recent clinical trials on primary RPLND for testicular seminoma highlight inaccuracies in conventional imaging for lymph node staging. Limited data exist on the accuracy of positron emission tomography (PET) in patients with chemotherapy-naïve testicular seminoma. We evaluated the accuracy of 18F-FDG PET for detection of metastatic disease within the SEMS trial (Surgery in Early Metastatic Seminoma). The SEMS trial is a phase II prospective study evaluating efficacy of primary RPLND in patients with testicular seminoma with limited retroperitoneal lymphadenopathy. 18F-FDG PET scanning was performed as a radiographic correlate in addition to standard axial imaging prior to surgery. PET findings were based upon local interpretation and results were compared to surgical pathology. Of the 55 patients enrolled in the trial, 26 (47%) underwent PET. Twenty (77%) scans were reported as positive with lymph nodes in the retroperitoneum, pelvis, or inguinal region. Of the positive PET scans, eighteen had pathologically positive lymph nodes (PPV 90%) at time of RPLND. Six PET scans were negative with five of these patients having surgically confirmed pN0 disease (NPV 83%). Sensitivity of PET for detecting lymph node metastatic seminoma was 95% and specificity was 71%. The average SUV of the PET positive lymph nodes and pathologically positive lymph node were 7.0 (range 2.6-18.8) and 6.8 (range 1.53-18.8), respectively. No PET positive lesions outside of the retroperitoneum or pelvis were found to represent metastatic seminoma on clinical follow-up. In patients with testicular seminoma, 18F-FDG PET findings correlated with both pathologically positive and negative retroperitoneal lymph nodes in the majority of cases. Further research is needed to determine if PET can improve upon the already good predictive performance of conventional imaging and clinical expertise.