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Case Reports

Abstract

We present a rare case of malignant melanoma with extensive neural differentiation and numerous Wagner-Meissner bodies. A Caucasian woman in her forties presented with a pigmented lesion on her left shoulder. Histopathologic examination of the excision specimen demonstrated a mostly intradermal proliferation comprised of two components: (i) a predominant “neurotized” component with numerous nodules displaying pale eosinophilic, fibrillary cytoplasm and peripherally oriented nuclei, consistent with Wagner-Meissner bodies, and (ii) a smaller population of nested epithelioid melanocytes. Based on these features, neurotized melanoma, collision of diffuse neurofibroma and melanoma, and cutaneous neurocristic hamartoma were in the differential diagnosis. Immunohistochemically, both components were reactive for SOX10, S100 protein, and PRAME. Both had loss of P16 expression. Melan-A and tyrosinase were positive only in the neurotized component. The mitotic rate was 2/mm². Notable chromosomal microarray findings included heterozygous loss of 9p22.1p13.1 (including CDKN2A/CDKN2B), and loss of 10q22.2q26.3 (including PTEN). In summary, these findings pointed towards a malignant melanoma showing extensive neural differentiation. It has been postulated that the melanocytes of melanoma can undergo transcriptional changes leading to altered expression of extracellular matrix proteins, resulting in a neural phenotype. Nevertheless, the neural phenotype with Wagner-Meissner bodies is rare. Wagner-Meissner bodies are considered relatively specific for diffuse neurofibromas, but have also been reported in facial/genital schwannomas, malignant peripheral nerve sheath tumors and as an incidental finding within the gastrointestinal tract. PTEN loss, a relatively rare event in melanocytic tumors, is a feature of malignant melanoma when present.