Scar Sarcoidosis as Presenting Finding in Pembrolizumab Induced Systemic Sarcoidosis in Stage III Melanoma: A Case Report

Immune checkpoint blockade using inhibition of Programmed Cell Death-1 (PD-1) improves both progression-free and overall survival in patients with advanced melanoma, but is associated with a unique set of toxicities termed immune-related Adverse Events (irAEs). We present a case of a man with stage IIIc melanoma who was treated with pembrolizumab (anti PD-1). Two months after initiation of the therapy, the patient developed subcutaneous nodules on his upper lip and right knee, both in a pre-existing scar. Histological examination showed non-necrotising granuloma, most consistent with sarcoidosis. PET-CT showed hypermetabolic mediastinal and hilar adenopathies as well as lung lesions and some cutaneous and subcutaneous metabolic hot spots. Bronchoscopy with biopsy of a lymph node confirmed the diagnosis of sarcoidosis. Pembrolizumab was withheld, whereby a gradual decrease and near spontaneous resolution of all lesions was seen over a period of approximately 6 months. The patient is currently in follow up with no evidence of disease recurrence.Our case shows a unique presentation of sarcoidosis in old scar tissue as presenting symptom of pembrolizumab-related systemic sarcoidosis and demonstrates the importance of histological examination of new lesions occurring during checkpoint inhibitor therapy in order to avoid misdiagnosis of melanoma progression.