Primary cutaneous interdigitating dendritic cell sarcoma is a morphologic and phenotypic simulator of poorly differentiated metastatic melanoma: A report of 2 cases and review of the literature.

Interdigitating dendritic cell sarcoma (IDS) is a rare form of hematologic malignancy associated with an aggressive clinical course. Only 4 prior cases have been described as originating in the skin. We encountered two male patients ages 47 and 61years of age who presented with solitary cutaneous neoplasms diagnosed as IDS. Histologic exam showed a coalescing nested and multinodular proliferation of large pleomorphic epithelioid cells. In one case an initial diagnosis of melanoma was rendered. A recurrence 8months later was then interpreted as a primary cutaneous IDS. This patient died of widespread metastatic disease within 2years from his initial surgery. The other patient has recently undergone wide excision and radiation without any recurrence or metastatic disease during this short follow up time period. Both patients had a tumor exhibiting the same phenotypic profile comprising leukocyte common antigen, SOX10, S100, CD68, and CD163 positivity. In reviewing the 4 other reported cases, there is a similar older male predominance (mean age of 58years) although women affected were significantly younger (mean age of 28years); there was a predilection for the proximal extremities and the face. Patients treated with excision only developed recurrent disease with one patient subsequently dying of metastatic disease. Primary cutaneous IDS is a highly aggressive hematologic malignancy that has many overlapping features with poorly differentiated epithelioid and spindle cell melanoma including SOX10 staining. An aggressive treatment protocol at the beginning could optimize patient survival.