Track: Case Reports

Topic: Melanocytic Neoplasms

Abstract:

Differentiating conventional cellular blue nevus from intermediate melanocytic neoplasms, so called melanocytoma, is often a histological challenge. To correctly classify these lesions, molecular studies are often warranted especially in melanocytic tumors with atypical clinical and histological presentations. A 21-year-old man was incidentally found to have an asymptomatic multinodular mass in his left flank. An excisional specimen of the lesion showed a poorly circumscribed melanocytic proliferation of predominantly epithelioid cells, extensively involving subcutaneous tissue. The melanocytes were diffusely and strongly positive for SOX10 and MART1. Mitotic figures were rare, and top-down maturation, necrosis and pleomorphism were absent. Cellular blue nevus was considered. However, histomorphology of poor circumscription and focal hypercellularity raised concern for a more aggressive lesion of intermediate melanocytic neoplasms. Next generation sequencing further revealed a likely pathogenic missense mutation in the PLCB4 (p.D630F) gene, supporting the diagnosis of blue melanocytoma. The majority of blue nevi harbor initial mutations in Gαq signaling pathway. The two most frequently mutated genes are GNAQ and GNA11 although mutations in CYSLTR2 and PLCB4 are also reported, the latter encodes the Gαq effector phospholipase Cβ4. More aggressive melanocytic lesions, including melanocytoma and melanoma, can emerge in the setting of a blue nevi accumulating additional molecular alterations. While the infiltrative nature of the lesion in the current case precludes complete excision and the patient is under interval imaging surveillance, complete excision is recommended in blue nevi associated with atypical features given their higher recurrence rate and potential progression.

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Sholeh Bazrafshan, MD, MS