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Case Reports

Abstract

Pigmented epithelioid melanocytoma (PEM) is a rare, low to intermediate grade melanocytic neoplasm, characterized by genetic alterations resulting in the activation of the protein kinase A pathway, usually through either PRKAR1A-inactivation or PRKCA fusion. Historically, they were classified as animal-type melanoma and later grouped with epithelioid blue nevi (EBN) of Carney Complex as they displayed overlapping histomorphologic features. A 12-year-old boy with a history of eczema presented with a longstanding 8 x 4 mm intermittently tender, slow growing, blue papule on his lower back. Shave biopsy showed a predominantly dermal proliferation of pigmented epithelioid and dendritic melanocytes associated with numerous melanophages and an occasional mitotic figure. The predominantly monomorphic epithelioid-shaped melanocytes, which contained a central nucleolus, formed central sheets with more interstitial growth towards the periphery, entrapping collagen bundles. A background nevus was not identified. The lesional cells were positive for SOX10, HMB45, and Cyclin D1 and negative for BRAF p.V600E. Ki67 showed a mildly increased proliferation index and a PRKAR1A stain showed loss of expression, suggestive of PRKAR1A inactivation. RNA sequencing analysis revealed a SCARB1::PRKCA gene fusion. The diagnosis of a PEM was rendered, and the patient underwent a wide local excision one month later. We herein report a rare case of a PEM with a PRKCA fusion which has been identified in younger-aged patients. Differentiating PEM from other heavily pigmented melanocytic lesions by incorporating histomorphology and molecular findings is crucial for accurate classification and to ensure appropriate treatment.