[Enlarged mediastinal lymph nodes of a patient with malignant melanoma stage IV under pembrolizumab treatment].

A 40-year-old patient with malignant melanoma pT4bN0M1a stage IV (AJCC classification 2017) was treated with the PD-1/PD-L1 antibody pembrolizumab. Three months after treatment initiation the patient developed enlarged mediastinal lymph nodes despite the partial response of the cutaneous metastases. An elective lymph node extirpation was performed. The histopathological result was consistent with a sarcoid-like reaction. Treatment was discontinued and a pulse therapy with systemic steroids led to a significant remission of the lymphadenopathy. This side effect can manifest both during PD-1/PD-L1 antibody and CTLA-4 antibody therapy and should be included in the differential diagnosis of mediastinal lymphadenopathy.