Clinical utility of FDG PET-CT in stage 1 and advanced testicular seminoma.

Abstract

5027 Background: Testicular seminoma is highly curable; however, treatments can cause long-term morbidity in survivors. Following chemotherapy for advanced seminoma, positron emission tomography with 2-[18F]fluoro-2-deoxy-D-glucose together with computerised tomography (PET-CT) can identify patients with residual masses who do not need additional treatment. Its role in detecting recurrence during active surveillance, particularly in patients with small indeterminate masses, is unknown. We assessed the clinical utility of PET-CT in testicular seminoma undergoing active surveillance for stage 1 disease and following curative-intent treatment for advanced disease. Methods: An institutional database was interrogated to identify patients with testicular seminoma who underwent PET-CT between 2000-2020. Demographic, clinicopathological, PET-CT findings and outcome data were retrieved. The positive predictive value (PPV) of PET-CT for correctly identifying disease recurrence was calculated, with disease recurrence (true positive) defined as progressive radiological change, response to treatment or histological confirmation. Negative predictive value (NPV) was calculated for correctly identifying non-recurrence (true negative) at 24-months post PET-CT. Results: We identified 193 PET-CT in 181 stage 1 patients. Of these, 18 (10%) PET-CT were positive, with all correctly diagnosing recurrence, PPV 100%. Of the 138 negative PET-CT with at least 24 months follow up, 5 recurrences developed, NPV 96%. In the subset of PET-CT conducted for suspicion of recurrence in stage 1 patients (n = 71: abnormal imaging n = 65, elevated markers n = 4, other clinical suspicion n = 2), 16 (23%) PET-CT were positive, with all correctly diagnosing recurrence, PPV 100%. In this subset, the NPV is 93% at 24 months (3 recurrences in 44 negative PET-CT). We also identified 154 PET-CT in 77 post-treatment, advanced stage patients. Of these, 69 (45%) PET-CT were positive, with 51 correctly diagnosing recurrence, PPV 74%. Of the 66 negative PET-CT with at least 24 months follow up, 5 recurrences developed, NPV 92%. In the subset of PET-CT performed for suspicion of recurrence following treatment for advanced disease (n = 61: abnormal imaging n = 49, elevated markers n = 5, other clinical suspicion n = 7), 41 (67%) PET-CT were positive, with 36 correctly diagnosing recurrence, PPV 88%. In this subset, the NPV is 94% at 24 months (1 recurrence in 17 negative PET-CT). Conclusions: At our centre, PET-CT has a very high PPV for recurrence, particularly in stage 1 disease, and a very high NPV for non-recurrence in all disease settings. In the subset of PET-CT performed for suspicion of recurrence, PPV is > 88% and NPV is > 93%. The role of PET-CT should be considered in patients with suspicion of recurrence where it may prevent over-treatment in up to 70% patients in stage 1 or 30% in advanced disease.