Maintenance Oral Etoposide After High-Dose Chemotherapy (HDCT) for Patients With Relapsed Metastatic Germ-Cell Tumors (mGCT)

Abstract

Background: HDCT and peripheral-blood stem-cell transplant (PBSCT) can cure up to 60% of pts with relapsed mGCT. Maintenance daily oral etoposide after salvage therapy has demonstrated potential clinical benefit. We now evaluate the potential role of maintenance etoposide versus observation post HDCT+PBSCT in this nonrandomized retrospective analysis.

Methods: The prospectively maintained Indiana University testicular cancer database was interrogated. Patients with relapsed non-seminoma who completed HDCT+PBSCT and achieved complete serologic remission and hematologic recovery were evaluated. Outcomes of pts who received maintenance etoposide (N = 141) were compared to pts who were observed (N = 242). In this retrospective study, Kaplan-Meier method was used to analyze progression-free survival (PFS) and overall survival (OS). Univariable and multivariable cox regression models were used to determine variables associated with PFS. We also performed an additional analysis to compare the survival outcomes in the platinum-refractory patients' subgroup based on maintenance etoposide treatment.

Results: Two-year PFS in the maintenance etoposide vs observation group was 55% vs. 46% (P = .028). Two-year OS was 61% vs 54% (P = .04). A multivariable analysis was performed, including the factors: primary tumor site (testis vs. mediastinum), IGCCCG risk, platinum refractory, HDCT line of therapy (2nd vs ≥3rd), tumor marker amplitude at HDCT initiation, and receipt of maintenance etoposide post HDCT vs. observation. Maintenance etoposide was confirmed as an independent predictor of improved PFS with HR 0.51 [95% CI, 0.37-0.70] (P < .001). Two-year OS and PFS for platinum-refractory patients who received maintenance etoposide vs. observation group were 50.2% vs. 26.1% (P < .0001) and 44.2% vs.. 23.1% (P = .0003), respectively. There was no statistically significant difference in 2-year OS and PFS between the platinum-sensitive patients who received maintenance etoposide and those who were observed.

Conclusion: Daily oral etoposide therapy produced encouraging efficacy results in patients with relapsed non-seminoma GCT (NSGCT) who completed HDCT and PBSCT and achieved complete serologic remission and hematologic recovery. Patients with platinum-refractory disease and poor prognostic features are potential candidates for daily maintenance oral etoposide post HDCT. These data have led to an ongoing randomized phase II clinical trial (NCT04804007).

Keywords: Germ cell tumors; Maintenance etoposide; Relapsed testicular cancer; Salvage chemotherapy; Testicular cancer.