Management of relapsed primary retroperitoneal (RP) germ-cell tumor (GCT) after front-line chemotherapy.

637 Background: Primary RP GCT represents a rare subset of extragonadal GCTs. While front-line therapy remains similar to gonadal GCT, there is limited data on management of relapsed disease for these patients (pts). Here, we describe management and outcomes of pts with relapsed primary RP GCT. Methods: The prospectively maintained Indiana University testicular cancer database was queried for patients with primary RP GCT who relapsed after first-line therapy between 1990-2024. Kaplan-Meier method was used to analyze progression free survival (PFS) and overall survival (OS). Survival outcomes based on type of second-line chemotherapy was compared using the log rank test. Results: 53 pts were included in the analysis. Median age at diagnosis was 33.7yrs (17.4-67.9). Primary tumor pathology was non-seminoma in 75.5% and seminoma in 24.5%. Predominant histology was seminoma (30.2%), mixed (26.4%), choriocarcinoma (17.0%), yolk sac tumor (13.2%), embryonal (9.4%), teratoma (3.8%). Other metastasis sites included pulmonary (56.6%), liver (35.9%), posterior mediastinum (15.1%), pelvic lymph nodes (13.2%), brain (13.2%), bone (9.4%). IGCCCG risk was good in 30.2%, intermediate in 15.1%, and poor in 54.7%. First-line chemo was BEPx4 (54.6%), VIPx4 (11.3%), BEP x3 (7.5%), EPx4 (7.6%), BEPx2 + HDCTx2 (2.0%), and other (17.0%). All 53 pts had progression of disease after first-line chemo. 44 received salvage chemotherapy, 5 received RPLND, 2 other salvage surgery, 1 radiation, and 2 received no salvage therapy. Salvage chemo was HDCT for 69.8% vs. standard salvage chemo for 30.2%. For pts treated with HDCT, 83% completed 2 cycles. 46.7% of those treated with HDCT progressed afterward. Of pts who had salvage RPLND, 3 were found to have teratoma and 2 had active GCT. 2 pts had other salvage surgery; 1 had thoracotomy with GCT and 1 had craniotomy with GCT. At time of last follow-up, 28.3% of all pts were alive with NED, 11.3% were alive with disease, 13.2% were lost to follow-up, and 47.2% had died of disease. The table lists PFS and OS by salvage chemo type. Conclusions: Patients with relapsed primary RP GCT seem to have worse outcomes compared with historical results from relapsed gonadal GCT. A subset of patients with relapsed primary RP GCT are curable with salvage therapy. Survival outcomes by salvage chemotherapy received. HDCT N=30 Standard dose chemo N= 14 p-value 2-yr PFS 47.7% (95% 28.7-64.5) 31.8% (95% 7.7-59.9) p=0.18 2yr OS 53.8% (95% 34.0-70.0) 68.6 (95% 30.5-88.7) p=0.84