Track: Case Reports

Topic: Melanocytic Neoplasms

Abstract:

A 13-year-old male presented with a long history of a dark streak in his right middle fingernail. Two years before the presentation, he noted that the pigmented area started to enlarge, and the nail bed began draining. He was treated with several courses of antibiotics, but after no resolution, he underwent an excisional biopsy. Histologic sections showed an ulcerated, polypoid proliferation of markedly atypical melanocytes with brisk mitotic activity (8 per square millimeter) and diffuse p16 loss. PRAME was negative. Next-generation sequencing studies revealed a fusion between exon 1 of ARL6IP1 and exon 6 of PRKCB, along with a high tumor mutational burden (8.09 vars/MB). Melanocytic lesions with protein kinase C (PRKC) fusions are a newly described category of melanocytic tumors. These neoplasms can vary from benign to malignant, typically involve younger patients, and have been described as having features of blue nevi, pigmented epithelioid melanocytes, and Spitz nevi. A recent study characterized a variety of melanocytic tumors with protein kinase C fusions, identifying a total of 14 different fusion partners. A fusion with ARL6IP1 has yet to be described in the literature. The patient ultimately underwent a partial amputation (final Breslow depth 5.0 mm) and a sentinel lymph node biopsy that showed metastatic disease. This case illustrates a new class of melanocytic tumors (PRKC fusions) and highlights a previously undescribed 5’ fusion partner.

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Lori Prok, MD