Abstract
An 11-year-old male presented with a six-year history of a solitary round, raised pigmented nevus on his left upper medial buttocks. It demonstrated interval growth and became pruritic with resulting skin breakdown from scratching. The child’s pediatrician clinically diagnosed it as a blue nevus, and a complete excision was performed. Pathology demonstrated a markedly pigmented melanocytic lesion extending through the dermis into the subcutis in a bulbous fashion. The lesional component was composed of cellular sheets and fascicles of spindled and ovoid nevus cells with focal areas with more epithelioid type cells. There were focal areas of necrosis and rare (1-3 per mm2) mitotic figures. The Ki-67 proliferation index was within normal limits. A p16 stain was difficult to evaluate due to the markedly pigmented lesional cells. Based on these histopathologic findings, a diagnosis of atypical cellular blue nevus was favored. However, given the presence of histopathologic features concerning for possible cutaneous melanoma, a next-generation sequencing (NGS) assay was performed. The NGS assay revealed a DNA variant of GNAQ (GNAQ c.626A>T (p.Q209L). GNAQ encodes a member of the trimeric G protein complex, which regulates the development and function of blood vessels. The Q209L GNAQ variant is present at a mutational hotspot of GNAQ and has been associated in primary leptomeningeal melanocytic neoplasms as well as blue dermal nevi. This variant has only very rarely been reported in cutaneous melanomas. No other mutations were identified, which further supported the benignity of the nevus. In our case, the elucidation of this Q209L GNAQ variant served in strong support of a diagnosis of atypical cellular blue nevus over cutaneous melanoma. This case demonstrates the importance of considering performing mutational analysis in similar cases of atypical cellular blue nevi demonstrating histopathologic features concerning for cutaneous melanoma.
Financial Disclosure:
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