Editor’s Note: During a recent oncology symposium, Dr. Jennifer King from Indiana University presented the results of a Phase II clinical trial (Abstract 587) evaluating cabozantinib in patients with relapsed/refractory germ-cell tumors (R/R GCT). This study explores the efficacy and safety of a multi-target tyrosine kinase inhibitor (TKI) in a patient population that has failed multiple lines of standard therapy.01 Clinical Rationale:
Addressing the Unmet Need in R/R GCT Approximately 20% of patients with metastatic GCT relapse following frontline therapy, and up to 50% will relapse after salvage chemotherapy. For those not cured by salvage regimens, therapeutic options are severely limited. Biological evidence suggests that increased VEGF expression, enhanced angiogenesis, and c-MET pathway activation play critical roles in GCT progression. Cabozantinib, a TKI targeting c-MET, VEGF, RET, and AXL, provides a mechanistic rationale for treating this refractory population.
02 Study Design:
A Simon Two-Stage Phase II Trial This was a Phase II, single-arm study utilizing a Simon two-stage design. Eligible patients included those with GCT who relapsed after frontline cisplatin-based therapy and at least one salvage regimen. Notably, patients with primary mediastinal non-seminomatous GCT and late-relapse disease were eligible. After an initial enrollment of 18 patients in Stage 1 met the efficacy threshold, the trial expanded to Stage 2, accruing a total of 44 evaluable patients. The primary endpoint was the clinical benefit rate (CBR), defined as the proportion of patients achieving a complete response (CR), partial response (PR), or stable disease (SD) for at least 3 months.
03 Patient Demographics:
A Heavily Pretreated Cohort The median age of the 44 evaluable patients was 34.2 years.
- Pathology: 95% of patients had non-seminomatous disease.
- Risk Profile: 47% presented with poor-risk disease at initial diagnosis; 40.9% had late-relapse disease.
- Prior Therapy: The median number of prior chemotherapy regimens was 4, with 63% of the cohort having previously received high-dose chemotherapy (HDCT).
04 Efficacy Outcomes:
Meaningful Disease Control With a median follow-up of 8.8 months, the study reached its primary endpoint:
- Clinical Benefit Rate (CBR): 43.2% (n=19). This included 2 patients with PR and 17 patients with SD for ≥3 months.
- Survival Data: Median progression-free survival (PFS) was 2.4 months, and median overall survival (OS) was 7.3 months.
- Durability of Response: The median duration of radiographic SD was 4.1 months. Furthermore, 46% of patients experienced a measurable decrease in tumor size.
- Tumor Markers: Reductions in AFP and HCG were observed in 88% and 59% of patients, respectively.
05 Safety and Tolerability:
Manageable Toxicity Profile The safety profile of cabozantinib in this population was consistent with its known effects in other solid tumors:
- Adverse Events (AEs): Diarrhea was the most common AE (predominantly Grade 1 or 2). Other AEs occurring in >25% of patients included fatigue, nausea, and hypertension.
- Dose Management: Dose reductions were required in 11 patients.
- Compliance: Critically, no patients discontinued treatment due to toxicity. The lack of overlapping toxicities with traditional cytotoxic agents suggests cabozantinib may be a safer alternative to further platinum-based cumulative toxicity.
Conclusion and Future Outlook Dr. Jennifer King concluded that cabozantinib demonstrates a clinically meaningful benefit rate of 43.2% in a heavily pretreated GCT population. Based on these encouraging results, an ongoing study is evaluating zanzalitinib in combination with oral etoposide. Pending safety confirmation, this combination will transition into the maintenance setting following salvage high-dose chemotherapy.
