Track: Case Reports

Abstract:

Collision tumors composed of a blue nevus and adnexal neoplasms such as trichoepithelioma or trichoblastoma are rare and may clinically resemble melanoma. We present the case of a 24-year-old female with a longstanding lesion on the lower back identified during routine skin examination. Histopathologic evaluation of a shave biopsy demonstrated a dermal proliferation of monotonous spindled melanocytes and nests of basaloid epithelium. The excision revealed a bulbous melanocytic proliferation with retained P16 and BAP1 expression, low proliferation index, and negative PRAME staining, supporting the diagnosis of a cellular blue nevus. Additional CK19 staining highlighted basaloid epithelium consistent with trichoepithelioma/trichoblastoma. MART-1 and H&E stains further characterized the lesion. This case emphasizes the importance of histologic assessment and clinicopathologic correlation in identifying rare benign neoplasms that may mimic malignancy.

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Leah Naasz