Primary retroperitoneal lymph node dissection for clinical stage IIA/B metastatic seminoma: A multi-centre Australian experience.

601 Background: Seminoma is highly chemo-sensitive and radio-sensitive. Contemporary guidelines describe chemotherapy and alternative radiotherapy regimens as standard treatment for clinical stage IIA/B metastatic seminoma. De-escalating strategies aim to maintain oncological safety whilst minimising treatment toxicity. Primary Retroperitoneal Lymph Node Dissection (RPLND) for retroperitoneum confined disease has emerged as an alternative to standard-of-care chemotherapy in this cohort. We present peri-operative and oncological outcomes of primary RPLND in an Australian context. Methods: Patients were identified in a prospectively maintained testicular cancer database (iTESTIS, Walter and Eliza Hall Institute, ACTRN12618000735257) who underwent primary RPLND between 2019-2025. All patients were chemotherapy-naïve with retroperitoneum confined retroperitoneal disease. RPLND were performed by two uro-oncologists in high-volume centres. Peri-operative outcomes, complication rates, recurrence free survival, pattern of relapse and adjuvant treatment were analysed. Results: A total of 20 patients were included, with a median age of 39.5 (IQR 35.5-4) and BMI of 25.1 (IQR 22.1-30.7). Median operative time, length of stay and estimated blood loss was 180 minutes (IQR 164.8-210.0), 1 night (IQR 1-2) and 75mL (IQR 50-100) respectively. One patient underwent open-RPLND after declining Robotic-Assisted RPLND (RA-RPLND). Histopathology confirmed seminoma in 18 patients and conversion to non-seminomatous germ cell tumour in 2 patients. One patient had chylous ascites requiring radiological drainage within 90-days of surgery. One patient underwent adjuvant chemotherapy for high-volume disease. After a median follow-up of 26 months (IQR 16-43), 4 patients had recurrence at 8, 9, 19 and 29 months post-operatively, with 2 in-field and 1 out-of-field recurrences, and 1 detected by rise in tumour markers only. The 2-year recurrence free survival in this cohort is 83.3%. Conclusions: Primary RPLND in clinical stage II metastatic seminoma is safe, and our outcomes are comparable with contemporary international data. Whilst further validation is required internationally, we support the integration of primary RPLND as an option in high-volume centres, to avoid toxicity and long term adverse effects associated with traditional treatments. Ongoing studies will clarify the long term oncological outcomes and further define the role of surgery in the contemporary management of metastatic seminoma.