Abstract

Immune checkpoint inhibitors (ICIs) have provided effective treatment options and changed the management algorithms for many malignancies. In addition to their anti-tumor efficacy, a broad array of immune-related adverse events has been recognized in associated with ICIs. Cutaneous adverse events occur in up to 30% of patients on ICIs, and commonly include pruritus, vitiligo, and lichenoid reactions. As ICIs have become more frequently used, an increasingly broad spectrum of uncommon associated cutaneous adverse effects has been observed. We present a case of an ICI-associated dermal granulomatous reaction mimicking sarcoidosis in a patient with metastatic melanoma. A 75-year-old male presented to dermatology clinic with a painful nodule on his left posterior shoulder. Biopsy demonstrated melanoma, Breslow thickness 1.65mm, without ulceration (pT2a), which was treated with wide local excision and sentinel lymph node biopsy (negative). Two years later, he presented with a firm, subcutaneous nodule in close proximity to his melanoma scar. Biopsy confirmed metastatic melanoma, which was treated with radical excision of the tumor followed by adjuvant pembrolizumab. After his second dose of therapy, he developed a firm, subcutaneous nodule on his right malar cheek. A punch biopsy revealed minimally inflamed, non-caseating granulomas within the superficial and deep dermis. Stains for microorganisms were negative. The findings were consistent with a sarcoidosis-like granulomatous reaction secondary to pembrolizumab. This reaction was likely caused by the activation of his immune system, which may also correlate with response to ICI therapy. This case demonstrates that firm subcutaneous nodules can present a diagnostic challenge in a patient with a history of metastatic melanoma. Dermatologists and pathologists should be aware of this uncommon cutaneous adverse event of ICI therapy.

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