A case of pseudoprogression in avelumab maintenance therapy for metastatic bladder cancer

INTRODUCTION: A unique phenomenon of immune therapy is pseudoprogression; however, a definite mechanism and predictive factors remain unclear. We herein report a case of pseudoprogression with avelumab maintenance therapy. CASE PRESENTATION: A 67‐year‐old male diagnosed with muscle‐invasive bladder cancer with lung metastasis was treated with four cycles of gemcitabine and cisplatin chemotherapy immediately after cystectomy and ileal conduit urinary diversion. The response to cisplatin‐based chemotherapy was a stable disease. Avelumab maintenance therapy was started after first‐line chemotherapy but was interrupted due to his general fatigue after the third administration of avelumab. At that time, computed tomography (CT) revealed an increased size of lung metastases. Two months after the interruption, avelumab maintenance therapy was restarted. At the end of the seventh dose of avelumab administration, CT showed a dramatic reduction of lung metastatic tumors. CONCLUSION: Pseudoprogression may also occur with avelumab maintenance therapy in metastatic bladder cancer.