Background: While the majority of patients with metastatic testicular cancer are cured with first-line cisplatin-based chemotherapy, 20-30% of patients will relapse following initial treatment. Many will still be cured with second and even third-line chemotherapy options, but there remains a need for new therapeutic approaches for patients with relapsed/refractory disease. Cabozantinib is an oral tyrosine-kinase inhibitor (TKI) with multiple targets including c-MET, VEGF, RET, and AXL. Testicular GCT have low rates of somatic mutations, though have been shown to be associated with a gain of chromosome 7, a portion of which encodes c-MET. When hepatocyte growth factor (HGF) binds to its c-MET receptor, cell proliferation, migration, invasion, and apoptosis escape occurs. In addition, compared to normal testicular tissue, testicular GCT have been shown to have higher rates of VEGF expression. Based on these findings, we proposed a phase 2 trial with cabozantinib in patients with relapsed/refractory GCT. Methods: This phase II, single arm, open label trial with a Simon two-stage design is evaluating cabozantinib 60mg daily in patients with relapsed/refractory GCT. Eligible patients are adult men and women with GCT (seminoma, non-seminoma, or ovarian GCT) that have progressed after first-line cisplatin-based combination chemotherapy in addition to at least 1 salvage regimen and are considered incurable with standard therapies. Patients with primary mediastinal non-seminoma, late relapse, and treated stable brain metastases are eligible. 12 patients will be enrolled initially in the first stage of the Simon two-stage design. If at least one complete response (CR), partial response (PR), or stable disease (SD) for ≥3 months is achieved, the trial will be deemed worthy of further investigation and 9 additional patients will be enrolled. Patients will be treated daily with cabozantinib until time of progression or unacceptable toxicity. Primary outcome is clinical benefit rate (proportion of CR, PR, and SD for ≥3 months using RECIST 1.1, modified to include tumor markers, AFP and hCG). Secondary outcomes include objective response rate, progression-free survival, overall survival, and tolerability and toxicity of cabozantinib. Exploratory evaluation of MET overexpression by IHC and amplification by next generation sequencing in correlation with response will be performed. This study is currently enrolling patients. As of September 20, 2021, the prespecified goal for the Simon stage 1 has been met, and 7 of planned 21 patients have enrolled. Clinical trial information: NCT04876456.