A Case of Avelumab-Resistant Upper Urothelial Carcinoma Responding to Pembrolizumab

In patients previously treated with immune checkpoint inhibitors (ICIs) for malignancies, the efficacy and safety of re-challenging with the same or another type of ICI remain unclear. We experienced a case in which a patient responded to pembrolizumab as a salvage treatment despite primary resistance to avelumab as a maintenance treatment for metastatic upper urinary tract urothelial carcinoma (mUTUC). A 69-year-old female presented with anemia and microscopic hematuria, diagnosed as mUTUC with lymph node metastases. After receiving avelumab maintenance therapy following platinum-based chemotherapy, there was no response at all. The previous chemotherapy was re-administered, but unfortunately, bone metastases were newly detected. We subsequently administered pembrolizumab to the patient, resulting in reductions in both the primary and metastatic tumors. Even if the patient has primary resistance to the anti-programmed death-ligand 1 (PD-L1) antibody avelumab, the anti-programmed cell death 1 (PD-1) antibody pembrolizumab, as an ICI rechallenge, could be a treatment option for a limited number of patients with metastatic urothelial carcinoma (mUC).