Track: Case Reports

Topic: Melanocytic Neoplasms

Abstract:

Melanoma ex blue nevus (MBN), or melanoma arising in blue nevus, comprises a rare group of cutaneous melanomas that arise within pre-existing blue nevi or seemingly de novo melanomas with blue nevus-like features. Blue nevi and MBNs are distinct from epidermal-derived common nevi /conventional melanoma, being more closely related to uveal melanoma, harbouring GNAQ and GNA11 driving mutations. Features favouring MBN over blue nevus include tumoural necrosis, cytologic atypia, and frequent mitoses. BAP1 inactivation is another distinguishing feature of malignancy, although only identified in half of reported MBNs. We present a case of melanoma arising in association with a pre-existing blue nevus from the right anterior shoulder of a 47-year-old male. The lesion was present for years, with recent growth prompting the patient to seek medical attention. The dermatologist’s clinical impression was of a possible pilomatricoma, but dermal pigmentation was noted at the time of the biopsy, raising the suspicion of a melanocytic process. Histopathological diagnosis was based on the finding of a dermal proliferation of atypical epithelioid melanocytes showing increased mitotic index and prominent PRAME expression arising in association with a pre-existing blue nevus. Our case showed retained BAP1 nuclear expression by immunohistochemistry. Molecular analysis for melanoma-associated mutations is pending. Interestingly, on further clinical inspection, the patient was noted to have three small blue nevus-like lesions on the scalp. Further clinical investigation, staging, and management are pending. Here, we highlight our approach and challenges in diagnosing this unique, rare entity.

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Leah Scott, MD