4521 Background: Residual disease is a frequent finding after chemo for metastatic seminoma. Watchful waiting is recommended for residual lesions < 3 cm or lesions ≥3 cm with negative PET. Data on the optimal management of PET positive residual lesions is lacking. Methods: A retrospective analysis within the G3 Group identified 91 patients (pts) from 9 countries with metastatic seminoma and residual PET positive lesions after chemo. Pts with elevated AFP ( > 2xULN) or non-seminomatous components at diagnosis were excluded. We analyzed the post PET management chosen and its impact on relapse and survival. Results: Median follow-up was 29 (IQR 10 – 64) months. Median age at diagnosis was 41 (range 19 – 69) years. The primary tumor was gonadal in 68 pts (76%), retroperitoneal in 12 pts (13%) and mediastinal in 10 pts (11%). Prior to chemo the median size of the largest metastasis was 10 (range 1.4 – 23) cm, 67 pts (74%) had elevated LDH and 51 pts (57%) elevated HCG. Median diameter of the largest residual mass was 4.8 (range 1.1 – 14) cm mainly located in the retroperitoneum (77%), pelvis (15%), mediastinum (16%) or lung (4%). Median time from last day of chemo to PET was 7 (IQR 4 – 10) weeks. Post PET management was repeated imaging in 46 pts (51%), resection in 32 pts (35%), biopsy in 9 pts (10%) and radiotherapy in 4 pts (4%). Histology of the resected specimen was necrosis only in 25 (78%) and vital seminoma in 7 cases (22%). No biopsy revealed vital seminoma. Relapses occurred after a median of 3.7 (IQR 2.5 – 4.9) months in 16 pts (18%): 2/9 (22%) after biopsy, 12/46 (26%) on repeated imaging and 2/32 (6%) after resection (one necrosis, one < 10% vital seminoma). Site of relapse was the area of residual disease in 14 pts (88%) and additional distant relapse (one bone, one lung) in 2 pts (12%). All relapsed pts received successful salvage chemo apart from one who died from treatment and two pts who are alive with ongoing treatment. Conclusions: PET positive post chemo residual lesions in seminoma pts are false positive in about 75%. Relapses in PET positive pts occur early and can be salvaged with chemo. Further analysis is needed to identify risk factors for relapse.
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