Postherpetic granulomatous dermatitis occurring in the setting of immune checkpoint inhibitor therapy: A case report.

We report a case of a 72-year-old man presenting with a 2-month history of a persistent, painful rash of the chest, axilla, and back. He had a history of recently resolved varicella zoster virus reactivation in the same distribution of the current rash and metastatic malignant melanoma treated with nivolumab and ipilimumab. The histopathology was consistent with granulomatous dermatitis (GD), and a diagnosis of postherpetic isotopic response manifesting as GD was made. Given the paucity of reported cases of postherpetic GD in the setting of treatment with immune checkpoint inhibitors (ICIs), we discuss the clinicopathologic features of this case and potential mechanisms by which ICIs may contribute to the development of granulomatous disease.

Altered Morphology and Immunohistochemical Characteristics in Metastatic Malignant Melanoma After Therapy With Vemurafenib.

Metastatic melanoma is traditionally diagnosed using classic morphologic features in addition to immunohistochemical studies. The authors report a case of metastatic malignant melanoma where both morphology and immunohistochemistry were altered after treatment. This 51-year-old patient presented with metastatic melanoma to the brain and axilla. Initially, both metastases showed classic morphology and diffuse staining with the pan-melanoma antibody cocktail. This cocktail is a combination of 3 antibodies commonly used to diagnose melanocytic neoplasms: Melan-A (MART-1), tyrosinase, and HMB-45. In combination, the cocktail is highly sensitive for detecting melanocytic neoplasms and is commonly used to diagnose metastatic melanoma. Her tumor was positive for the BRAF 1799T>A (V600E) mutation, and she was treated with BRAF inhibitor therapy (vemurafenib). However, the axillary tumor recurred after treatment with vemurafenib. The recurrent tumor showed a markedly different morphology and complete loss of staining with the pan-melanoma antibody cocktail. This loss of staining accompanied by the change in morphology was an observation not previously documented after therapy with vemurafenib. This case demonstrates a potential pitfall in the diagnosis of metastatic or recurrent malignant melanoma.