Post-chemotherapy retroperitoneal lymph node dissection for patients with metastatic pure seminoma.

611 Background: Post-chemotherapy retroperitoneal lymph node dissection (pcRPLND) for metastatic testicular seminoma is reserved for highly select cases and can be associated with significant morbidity. We report contemporary outcomes of pcRPLND in patients with metastatic pure seminoma with the goal of better defining patient selection for surgery and exploring gaps in diagnostic staging. Methods: Patients who underwent pcRPLND after ≥1-line of chemotherapy for metastatic pure seminoma at our institution between 2000-2024 were included. Clinicopathologic, radiographic, perioperative, oncologic, and survival outcomes are reported. Results: 52 patients underwent pcRPLND for metastatic pure seminoma during the study period. Most patients (67%) received ≥2 lines of chemotherapy prior to surgery. Eight patients (15%) harbored residual viable seminoma at pcRPLND (Table), 38% and 6% following first-line and ≥2-lines of chemotherapy, respectively. None of the patients that received high-dose chemotherapy (TI-CE) had viable disease at surgery. Over a median follow up of 50-months, 5 (10%) patients relapsed after pcRPLND, all of whom had viable residual seminoma at pcRPLND. Of the 8 patients with residual seminoma at pcRPLND, 2 were cured with pcRPLND alone, 3 with pcRPLND plus additional chemotherapy, and 3 died from progressive disease. Conclusions: The risk of finding viable residual seminoma at pcRPLND varied based on prior chemotherapy received. These data underscore the importance of careful patient selection given the competing risks of morbidity associated with pcRPLND, the high likelihood of cure with high-dose chemotherapy, and the need for better diagnostics to guide surgical decision-making in this setting. Patients with residual seminoma at pcRPLND (N=8). ID Age a CS IGCCCG risk Chemo. PET/CT (pre-pcRPLND) No. (+) nodes Pathologic node size (cm) Adjuvant chemo. Time to relapse (mo.) Relapse location b Salvage therapy Survival I 40 III Intermediate BEPx3 Negative 1 7.3 EPx2 12.8 Unk. Unk. DOD II 49 II Good EPx4 Positive>3cm 1 0.8 No 4.2 SH, SR TIPx4 NED III 33 II Good EPx4 - 2 0.4 No - - No NED IV 36 I Good EPx4 Positive<3cm 1 2.1 No 12.1 SH TIPx4 NED V 42 II Good BEPx3 Positive<3cm 1 2.2 TIPx4 - - No NED VI 25