A Rare Case of Cutaneous Interdigitating Dendritic Cell Sarcoma

Abstract

Interdigitating dendritic cell sarcomas are aggressive tumors of dendritic cells, often presenting with lymphadenopathy. Fewer than ten cases of primary cutaneous IDCS have been reported. Histopathologically, IDCS presents as atypical spindle cells with irregular nuclei, and thus can be difficult to distinguish from melanoma, follicular dendritic cell sarcoma, and Langerhans cell tumors by H&E examination alone.1,2 We report a unique case of a man with cutaneous IDCS that was initially misdiagnosed as melanoma. Having previously undergone an excision of a reported “melanoma” on the neck, he presented with a new growth on the cheek. Histopathologic findings revealed an atypical dermal lymphohistiocytic infiltrate around vessels and cells forming nests along the dermal-epidermal junction. Immunohistochemical stains were strongly positive for S100, fascin, and lysozyme, whereas CD1a, langerin, CD21, CD23 and SOX10 were negative. These immunohistochemical findings were consistent with IDCS, and the patient's prior biopsy was then revisited. Similar staining revealed that lesion to also be a cutaneous IDCS. Follow up imaging with PET scan was negative for metastases, supporting the diagnosis of primary cutaneous IDCS. Our findings contribute to the limited literature on cutaneous IDCS and highlight a potential pitfall in its diagnosis due to overlapping histopathologic features with melanoma.

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