A Curious Case of Diabetic Ketoacidosis Secondary to Avelumab

Immune checkpoint inhibitors (ICIs) have completely changed cancer treatment in the last decade and are now widely used in several cancers. In the era of immunotherapy, oncologists have changed not only the way they evaluate treatment efficacy but also the management of treatment-related adverse events. This new profile of immune adverse events has resulted in an urgent need for a more holistic view of cancer patients and for more collaborations with other organ specialists to optimize patient treatment and support. The anti-programmed death-ligand 1 antibody, avelumab, has been widely used as a maintenance treatment in stage IV urothelial carcinoma since the results from the Javelin 100 bladder trial were published. We report a case of a 75-year-old man with stage IV urothelial carcinoma submitted to first-line platinum-based chemotherapy followed by maintenance avelumab. He achieved a complete bone and pulmonary response 10 months after stopping avelumab, which was suspended due to a serious immune adverse event, an ICI-induced type 1 diabetes mellitus. At present, the patient has an overall survival of 24 months and shows no evidence of disease with a good quality of life 16 months after avelumab suspension. We hypothesized that a late response to avelumab could explain this unexpected outcome.