Abstract

Periocular melanomas make up a rare subset of eyelid tumors and constitute less than one percent of all cutaneous malignant melanomas. We present a challenging case of a quickly growing eyelid tumor presented for pathologic evaluation via small punch biopsy. Histologic evaluation showed small, basophilic, somewhat plasmacytoid, and focally spindled tumor cells, negative for most markers of differentiation except CD99 (strong), CD138 (strong), S100 (subset) and Microphthalmia transcription factor (MITF) (weak). Furthermore, other specific melanoma markers were negative. The small sample size and patchy IHC markers increase the case complexity and while not entirely specific, were suggestive of a dedifferentiated malignant melanoma. Subsequent review of the excision specimen revealed additional patchy positive staining with melanocytic markers. A performed PRAME showed diffuse strong positivity within tumor as well. Melanocytic markers are known to have varying degrees of sensitivity and specificity but are usually expressed to some degree in melanocytic neoplasms. MITF, for example, is often positive but lacks specificity for melanoma. Additionally, cross reactivity can also be seen, e.g., CD138 a widely used as a plasma cell marker and CD99 have been reported to be positive in melanomas. Even PRAME, which is most often used to distinguish benign melanocytic proliferations from melanoma, may stain other non-melanocytic tumors. For difficult cases a holistic approach may provide important clues to the correct diagnosis; this involves open communication with the treatment team and fellow pathologists, a careful overview of the differential diagnosis to include tumor probability analysis, and careful review of IHCs.

Financial Disclosure:
No current or relevant financial relationships exist.