Primary Cutaneous Interdigitating Dendritic Cell Sarcoma: A Case Report and Review of the Literature.

Interdigitating dendritic cell sarcoma (IDCS) is a rare tumor of spindle to ovoid cells intermixed with lymphocytes and plasma cells. Primary cutaneous IDCS, with no nodal or other organ involvement is extremely rare, with less than 10 cases reported to date. Herein, the authors describe a case in which a 61-year-old man presented with scattered subcutaneous nodules on his left shoulder and right anterior thigh. A biopsy was performed, and the histopathologic findings revealed prominent, diffuse superficial, and deep dermal infiltration by an atypical epithelioid-shaped tumor forming sheets and cords infiltrating throughout the dermis. Immunohistochemical stains were strongly and diffusely positive for S100, CD45, CD68, and lysozyme, whereas CD21, CD23, CD3, CD20, CD30, CD34, and CD117 were all negative. The histologic and immunohistochemical findings were consistent with an IDCS. A positron emission tomography scan was negative for metastases, leading to the diagnosis of primary cutaneous IDCS. The patient was started on chemotherapy with gemcitabine and docetaxel, and was stable at 4 months follow-up. Our findings contribute to the limited existing literature on primary cutaneous IDCS. This is the first documented case in which chemotherapy with gemcitabine and docetaxel was implemented for treatment, helping to establish an optimal treatment protocol for clinical remission.