Clinical Benefit from Tyrosine Kinase Inhibitors in Metastatic Merkel Cell Carcinoma: A Case Series of 5 Patients

Case series Patients: Male, 58 • Male, 65 • Male, 75 • Male, 61 • Male, 69 Final Diagnosis: Merkel cell carcinoma Symptoms: Metastatic disease Medication: Pazopanib • Cabozantinib Clinical Procedure: Systemic therapy Specialty: Oncology OBJECTIVE: Rare disease BACKGROUND: Merkel cell carcinoma (MCC) is a rare but aggressive neuroendocrine skin cancer. The estimated 5-year survival of patients with metastatic disease is approximately 14%. Cytotoxic chemotherapy is associated with a modest median progression-free survival (PFS) of only 3 months. In recent studies, immunotherapy with anti-PD-1/anti-PD-L1 antibodies has demonstrated a high response rate in immunocompetent patients (>50% in chemotherapy-naïve patients) and responses are typically durable. However, approximately 50% of immunocompetent patients do not respond to immunotherapy. In addition, immunosuppressed patients have limited therapeutic options. Hence, there is a significant unmet need for effective treatments in these subpopulations. CASE REPORT: We describe 5 patients (out of 24 total) with metastatic MCC who were treated with a vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitor (TKI), either pazopanib (n=4) or cabozantinib (n=1), with clinical benefit. One patient had a complete response to pazopanib after 3 months of therapy. Four patients had stabilization of disease that lasted from 5 months to 3.5 years. In an immunosuppressed patient with psoriatic arthritis, stabilization of MCC was also associated with improvement in his arthritis that allowed cessation of immunosuppression. Patients did not develop any unusual toxicities from VEGFR-TKIs. CONCLUSIONS: Treatment with VEGFR-TKIs demonstrated clinical benefit in this selected small group of patients with metastatic MCC. Prospective investigation of VEGFR-TKIs is warranted in this population, especially in patients with disease refractory to immunotherapy.