Efficacy of Cabozantinib in Metastatic Papillary Renal Cell Carcinoma Following Ineffective Treatment With Initial Therapy of Nivolumab and Ipilimumab.

Sunitinib is listed as first-line therapy for non clear-cell renal cell carcinoma (RCC) in several guidelines. However, in the era of immunotherapy, there is an urgent need for updated evidence for the treatment of metastatic non clear-cell RCC. Herein, we present three cases of patients with type 2 papillary RCC who were effectively treated with cabozantinib. The first case was a 48-year-old woman who underwent radical nephrectomy (pT3aN0M0). The tumor relapsed in the retroperitoneum 3 months postoperatively and was unresponsive to first-line nivolumab plus ipilimumab (NI). After the use of cabozantinib, the tumors drastically shrunk in 2 weeks, and complete response was achieved 3 months later. The second case was a 55-year-old man who underwent radical nephrectomy (pT3aN2M1). Metastatic lesions continued to grow with first-line NI, and cabozantinib was used as the second-line therapy. All metastatic lesions had shrunk by 50% after 4 months. The third case was a 36-year-old man with multiple tumors in the left solitary kidney and iliopsoas muscle metastasis. First-line therapy with NI was ineffective; subsequently, second-line axitinib was used for 5 months, and the disease was identified as progressive. Cabozantinib was started as third-line therapy. Multiple tumors shrunk in 2 weeks. There is little evidence concerning the treatment of papillary RCC. We experienced low efficacy of NI for first-line treatment of papillary RCC for three patients who were subsequently effectively treated with cabozantinib. Cabozantinib inhibits multiple tyrosine kinase receptors, which may suppress aggressive tumor progression of type 2 papillary RCC. Cabozantinib or combination with immuno-oncological drugs may be a promising treatment option for papillary RCC.