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Case Reports

Abstract

Deep penetrating nevi (DPN) and atypical DPN/melanocytomas are classically indolent melanocytic lesions that exist within the differential of heavily pigmented cutaneous lesions along with blue nevi, cellular blue nevi, spindle cell nevus, and melanoma. We present two patients with atypical deep penetrating nevi (melanocytoma) that demonstrated positivity for PRAME. Patient 1 is a 42-year-old male with a pigmented lesion on the face and patient 2 is a 36-year-old male with a dark blue papule on the cheek. Lesional biopsies in both cases revealed a predominantly dermal neoplasm composed of enlarged atypical spindled and epithelioid melanocytes with abundant pigmented cytoplasm. An associated second melanocytic population of bland appearing melanocytes with appropriate maturation was evident in Patient 2. Significant mitotic activity was not appreciated. Immunohistochemistry demonstrated positivity in atypical melanocytes for PRAME (diffuse) and beta-catenin (diffuse nuclear staining in Patient 1; focal nuclear staining in Patient 2). Next-Generation Sequencing revealed CTNNB1, BRAF V600E, GABRA6 and TCCFBR2 mutations in Patient 2. Given the atypical features in concert with immunohistochemical and molecular genetic features, complete surgical excision was recommended in both cases. PRAME is an immunohistochemical marker that can aid in delineating melanoma from benign melanocytic lesions. Existing literature has characterized DPN and atypical DPN/melanocytomas as primarily PRAME-negative. These cases, however, stand in contrast to the reported pattern of negative staining for PRAME in these melanocytic lesions. The clinical implications of PRAME-positivity in atypical DPN/melanocytomas remain unclear and further complicate the predominating perceptions of PRAME immunohistochemistry as a useful tool in characterizing melanocytic proliferations.