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Diagnosis of Sarcomatoid Melanoma by Surrogate Immunostains

Fraga, Garth R., MD

The American Journal of Dermatopathology: April 2018 - Volume 40 - Issue 4 - p 304–305
doi: 10.1097/DAD.0000000000000993
Letters to the Editor

Department of Pathology, University of Kansas School of Medicine, Kansas City, KS

The author declares no conflicts of interest.

To the Editor:

I would like to express my thanks to Erstine et al for their helpful advice regarding diagnosis of sarcomatoid melanoma.1 I recently encountered a case of sarcomatoid melanoma, which confirmed the importance of histologic evaluation of the lesion's edge. I write to corroborate their findings, report a new case of sarcomatoid melanoma, and describe the use of surrogate immunostain markers for melanocytes for diagnosis of sarcomatoid melanoma. The case summary follows below:

A 75-year-old white man was referred by his primary care physician to a general surgeon for excision of an ulcerated 1.2 × 1.0-cm tumor of the skin of the scalp. It was removed en bloc through direct excision. Histologic sections demonstrated a raised, ulcerated tumor comprised large, pleomorphic plump spindled cells set in an inflammatory myxoid and hypervascular stroma. These cells exhibited florid cellular atypia with bizarre nuclei. The adjacent skin contained a proliferation of SOX10/Melan A-positive melanocytes which infiltrated adnexa and the superficial dermis and met criteria for conventional melanoma arising in the sun-damaged skin (Fig. 1). The large pleomorphic cells were nonreactive with Melan A and SOX10 and avidly expressed CD10. A few of the pleomorphic cells showed weak, equivocal cytoplasmic S100 protein signal. These findings raised the differential of a collision tumor of melanoma and atypical fibroxanthoma versus sarcomatoid dedifferentiation in pre-existent melanoma. CD56 and WT1 immunostains were obtained to resolve the diagnostic dilemma. They demonstrated convincing reactivity in the large pleomorphic cells, and a diagnosis of sarcomatoid melanoma was made (Fig. 2).





I found this case to be instructive because (1) without the lesion's edges, it could easily have been misinterpreted as an atypical fibroxanthoma and (2) it highlights the role that surrogate melanocyte immunostains can play in diagnosis of sarcomatoid melanoma. Previous investigators have used next-generation sequencing analysis and electron microscopy to determine etiologic associations between undifferentiated spindle cell tumors commingled with melanoma.2,3 These methods may not be available in some laboratories. Use of alternate immunostains such as WT1 and CD56 might bridge the practice gap in these situations. Avid cytoplasmic WT1 signal has been described in melanoma, and the antibody has been recommended for diagnosis of desmoplastic melanoma.4,5 CD56 expression has been reported in a small number of melanomas.6,7 Although neither marker is specific for melanocytic lineage, they may lend support to the diagnosis of sarcomatoid melanoma when more specialized analytic techniques are not available.

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7. Chu PG, Arber DA, Weiss LW. Expression of T/NK-cell and plasma cell antigens in nonhematopoietic epithelioid neoplasms. Am J Clin Pathol. 2003;120:64–70.
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