Metastatic pure seminomas with early relapse: Prognostic roles of high dose chemotherapy and surgery of residual disease.

5031 Background: Metastatic seminomatous germ cell tumors (mSGCT) are a rare form of cancer. Few studies focused on early relapse (< 12 months) after first-line chemotherapy (ChT). We aimed to evaluate the impact of salvage retroperitoneal lymph node dissection (RPLND), and high-dose ChT with hematopoietic stem cell transplantation (HDCT-HSCT) in mSGCT patients in a situation of early relapse. Methods: Ninety-one mSGCT patients treated between 2005 and 2022 in 7 French expert centers for an early recurrence after an initial favorable response to 1st-line ChT were retrospectively included. Patient clinical characteristics, progression-free survival after first relapse (PFS) and overall survival (OS) were evaluated. We also assessed the role of HDCT-HSCT as first salvage treatment, and the impact of complementary RPLND after salvage ChT. Results: After a median follow-up of 56 months, 3-year PFS and OS rates were 77.6% (95%CI, 68.3-88.1) and 88.4% (95%CI, 81.0-96.4), respectively. HDCT-HSCT was not associated with longer PFS or OS compared to standard-dose 2 nd -line ChT. In contrast, patients who underwent RPLND after salvage ChT demonstrated significantly longer PFS (at 3-years: 97.1% vs 63%; HR 0.15; 95%CI 0.03-0.65; p=0.012) and a notable trend towards improved OS (at 3-years: 97.0% vs 81.8%; HR 0.15; 95%CI 0.02-1.23; p=0.078). Conclusions: In mSGCT patients with first-year relapse, RPLND after salvage treatment is correlated with longer PFS and tends to be associated with longer OS. Identification of a subpopulation that might benefit from HDCT-HSCT ought to be performed since it did not confer survival benefits in the overall population.