Hyperprogressive disease after avelumab maintenance therapy in a patient with advanced ureter cancer: A case report.

In the early stages of immunocheckpoint inhibitor administration, we should be aware of rapid cancer progression, known as hyperprogressive disease, in real-world clinical practice. We report a case of a 73-year-old man who presented with right abdominal pain and was diagnosed with advanced right ureteral cancer involving the duodenum. He received four cycles of chemotherapy with gemcitabine plus cisplatin, followed by maintenance with avermab. After two cycles of avermab within a month, his primary cancer dramatically progressed and he died. This is the first report of a case in which unresectable ureteral cancer caused hyperprogressive disease after avelumab maintenance therapy.