2-18fluoro-deoxy-d-glucose positron emission tomography (FDG-PET) for postchemotherapy seminoma residuals: A retrospective validation of the SEMPET trial.

Abstract

4581 Background: The use of FDG-PET for the evaluation of postchemotherapy seminoma residuals has been recommended by several international guidelines. This is based on the prospective SEMPET trial including 56 PET studies. Our trial was designed to confirm these recommendations in a larger group of patients. Methods: Investigators from Europe and Canada were invited to contribute consecutive patient data. The eligibility criteria included: metastases of pure seminoma (testicular or extragonadal), negative tumor markers after first line or salvage platinum-containing chemotherapy (completed after 2001), CT evidence of clearly measurable residual masses ≥ 1cm in diameter after chemotherapy, a postchemotherapy FDG-PET scan evaluated by visual interpretation; and a follow-up of ≥ 24 months (unless relapse) or surgery of residual lesions. Results: By October 2009, 147 FDG-PET results from 17 institutions were contributed, of which 42 were ineligible, mostly due to insufficient follow-up (88%), 13 were rated equivocal and were not included in the final analysis. Interestingly, all patients with equivocal scans remained relapse-free. The results of the remaining 92 PET studies demonstrated 64 true negative (TN), 8 true positive (TP), 4 false negative (FN) and 16 false positive (FP). The interval between chemotherapy and PET scan was inadequate according to the current guidelines in 10/16 (63%) FP and in 2/4 (50%) FN scans. Excluding scans with inadequate timing, specificity, sensitivity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were 91%, 80%, 57%, 97%, and 90%, respectively. Eight of 45 (18%) residual lesions ≥ 3cm contained viable tumor; 42/45 (93%) were correctly predicted by FDG-PET. Conclusions: These retrospective data confirm a high specificity, sensitivity, and NPV of FDG-PET for the evaluation of postchemotherapy seminoma residuals. Based on a small number of positive PET scans, the PPV was less reliable than previously reported. However, FDG-PET performed within the correct timeframe remains a valuable tool for clinical decision-making in this clinical setting, and allows to omit unnecessary surgery. No significant financial relationships to disclose.