A rare case of cutaneous interdigitating dendritic cell sarcoma

Area of Science:

• Dermatopathology
• Oncology
• Immunohistochemistry

Background:

• Interdigitating dendritic cell sarcoma (IDCS) is a rare and aggressive neoplasm of dendritic cells.
• Primary cutaneous IDCS is exceptionally uncommon, with fewer than 10 reported cases.
• Distinguishing IDCS from other spindle cell tumors, such as melanoma, can be challenging based on H&E morphology alone.

Observation:

• A case of a man with a cutaneous IDCS initially misdiagnosed as melanoma is presented.
• Histopathology revealed atypical dermal lymphohistiocytic infiltrate with nests at the dermal-epidermal junction.
• Immunohistochemistry showed positivity for S100, fascin, and lysozyme, with negativity for CD1a, langerin, CD21, CD23, and SOX10.

Findings:

• The immunohistochemical profile confirmed the diagnosis of IDCS.
• Re-examination of a prior biopsy specimen also identified it as cutaneous IDCS.
• PET scan indicated no evidence of metastases, supporting a primary cutaneous origin.

Implications:

• This case underscores the diagnostic difficulties in differentiating cutaneous IDCS from melanoma.
• Accurate diagnosis relies on a combination of histopathology and specific immunohistochemical markers.
• Understanding these overlapping features is crucial for appropriate patient management and treatment of this rare cutaneous malignancy.