Immunotherapy pitfall: sarcoid-like reaction mimicking disease progression in advanced melanoma treated with nivolumab

Summary Immunotherapy is the first-line treatment in many solid cancers. Immune system activation leads to specific immune-related adverse events (irAE), which also include the rare sarcoid-like reaction (SLR). In imaging studies SLR can mimic cancerous lesions. Even though patients suffering from SLR are mostly asymptomatic and do not need antisarcoidosis therapy, it is crucial to not misdiagnose irAE as disease progression and unnecessarily discontinue vital immunotherapy. However, SLR should be considered at any point if disease progression is suspected. In addition, the diagnosis of SLR can only be confirmed histologically. In this case report, we want to highlight the clinical relevance of recognizing SLR in a patient with advanced melanoma treated with nivolumab and emphasize the importance of rebiopsy in case of suspected disease progression.