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

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).

Phase II trial of brentuximab vedotin in relapsed/refractory germ cell tumors

Background CD-30 is highly expressed in some patients with non-seminomatous germ-cell tumors. Brentuximab vedotin is an antibody-drug conjugate directed to CD-30. We report a phase 2 trial of brentuximab vedotin in patients with chemo-refractory GCT. Patients and methods This is a single arm, two cohort phase 2 trial investigating brentuximab vedotin 1.8 mg/kg IV every 3 weeks until disease progression or intolerable toxicities in patients with relapsed GCT who have no curative options. Patients with mGCT who progressed after first line cisplatin-based chemotherapy and after at least 1 salvage regimen (high-dose or standard-dose chemotherapy) were eligible. CD30 expression was assessed and two cohorts defined: CD30 positive and CD30 negative/unknown. Results 18 patients were enrolled. Median age 34.7 (range, 23-56). All patients had non-seminoma. Median AFP 4.9 (range, 1-219,345) and hCG 282 (range, 0.6-172,064). Five patients had late relapse (> 2 years). Median number of previous chemotherapy regimens was 3 (range, 2-7). Ten patients received prior high-dose chemotherapy. Seven patients had positive CD30 staining. There were two grade 3 treatment-related adverse events. No partial or complete responses were observed. 6 patients achieved radiographic stable disease (range, 9-14.9 weeks), 5 had elevated AFP or hCG at trial entry and all 5 had transient > 50% decline in baseline AFP/hCG: 4 had CD30 -ve and 2 had CD30 + ve staining; 10 patients had progression of disease as their best response; 2 were not evaluable for response. Conclusion Brentuximab vedotin does not appear to have clinically meaningful single-agent activity in patients with refractory GCT.