Abstract
INTRODUCTION: Immunotherapy-based combinations have become the standard first-line therapy for metastatic renal cell carcinoma. However, combined immunotherapy for renal collecting duct carcinoma had been reported, but its therapeutic efficacy had been unclear. CASE PRESENTATION: The first case was a 62-year-old man treated with pembrolizumab and axitinib for renal collecting duct carcinoma with multiple bone metastases. After 7 months, the primary and metastatic lesions shrunk and were evaluated as a partial response. The second case was a 71-year-old man treated with pembrolizumab and axitinib for renal collecting duct carcinoma with lymph node and lung metastases. After 9 months, the primary and metastatic lesions shrunk and were evaluated as a partial response. In both cases, the tumor cell expression of programmed death ligand-1 was negative, and CD4(+) and CD8(+) cells were observed in the tumor. CONCLUSION: Combined immunotherapy with pembrolizumab and axitinib may be effective for metastatic renal collecting duct carcinoma.