Sarcoidosis post-anti-PD-1 therapy, mimicking relapse of metastatic melanoma in a patient undergoing complete remission

Novel treatments of metastatic melanoma include the usage of checkpoint inhibitors such as anti-cytotoxic-T-lymphocyte-associated antigen (CTLA-4) or anti-programmed death-1 (PD-1) antibodies, which are immunomodulatory antibodies that enhance the immune response against tumors. While they have substantially improved the prognosis for patients, these therapies are associated with a large spectrum of immune-related adverse effects (irAEs). We report a patient developing pulmonary and cutaneous sarcoidosis after pembrolizumab therapy while complete regression of stage IV melanoma was perceived. Coincident development of sarcoidosis and metastatic melanoma as illustrated by this case report poses a diagnostic challenge because, in contrast to other irAEs, both diseases share common features such as pulmonary lesions, hilar adenopathies and skin nodules. Considering sarcoidosis as a potential side-effect of pembrolizumab treatment is crucial to avoid misdiagnosis with malignant lesions, hence careful description and reporting of such cases is primordial for patient care and may also provide us with insightful knowledge on the pathogenesis of immune-related diseases.