Track: Case Reports

Topic: Melanocytic Neoplasms

Abstract:

NRAS hot spot mutations are driver mutations associated with common melanocytic nevi. Herein, we describe a case of NRAS-mutant melanocytic nevus with a blue nevus-like morphology. A 71-year-old Japanese man presented with a 4.6-mm nodule on the back. Histopathological examination revealed a dense distribution of spindle-shaped and dendritic melanocytes, mainly in the upper dermis. Vertical periadnexal extension reached the deep dermis at the center of the tumor. Mild nuclear atypia, no mitotic figures, massive melanin pigmentation, a marked infiltrate of melanophages, a sclerotic collagenous stroma, and a small junctional component were observed. These findings are similar to the characteristics of compound type blue nevus, so-called “Kamino nevus”. Immunohistochemical examination revealed no PRAME expression and preserved p16 expression. Diffuse RASQ61R immunoreactivity was observed in these tumors. Targeted DNA sequencing revealed NRAS (Q61R) mutation. Other pathogenic mutations in BRAF, GNAQ, GNA11, CTNNB1, PRKAR1A, or other kinase fusion genes were not identified. Thus, we considered this tumor to be on the spectrum of a common melanocytic nevus, but not on that of a blue nevus. Morphologically, NRAS-driven melanocytic nevi can resemble blue nevi.

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Tsubasa Hiraki, MD, PhD