BackgroundCollecting duct carcinoma (CDC) of the kidney is associated with an aggressive course, limited response to treatment, and poor prognosis. Platinum-based chemotherapy is currently recommended as the first-line treatment in patients with metastatic CDC. Accumulating evidence supports the use of immunotherapy with checkpoint inhibitors as second-line therapy.Case presentationIn this case report, we describe the first case of avelumab administration due to disease progression during chemotherapy with gemcitabine and cisplatin in a Caucasian, 71-year-old man presenting with multiple metastases due to CDC of the kidney. The patient initially responded well to four cycles of chemotherapy and his performance status improved. After two additional chemotherapy cycles, the patient presented with new bone and liver metastases (mixed response to chemotherapy with an overall 6-month progression-free survival). We offered him avelumab as a second-line treatment in this setting. The patient received a total of three cycles of avelumab. The disease remained stable (no new metastases during treatment with avelumab), and the patient developed no complications. To alleviate his symptoms, radiation therapy for the bone metastases was decided. Despite successful radiation of the bone lesions and further improvement of symptoms, the patient developed hospital-acquired pneumonia and died approximately ten months after the initial diagnosis of CDC.ConclusionsOur findings suggest that the applied treatment modality with gemcitabine and cisplatin chemotherapy followed by avelumab was effective in terms of both progression-free survival and quality of life. Still, further studies assessing the use of avelumab in this setting are mandatory.