[535] Interdigitating Dendritic Cell Sarcoma of the Skin: A Rare and Challenging Malignant Tumour That Demonstrates a Distinctive Dendritic Pattern of Staining with WT-1 and CD99

S Sade, AS Al-Habeeb, D Ghazarian. University Health Network, Toronto, ON, Canada

Background: Interdigitating dendritic cell sarcoma (IDCS) is a rare malignant tumour representing less than one percent of hematogenous malignancies. Its occurrence in extranodal sites is extraordinarily rare and these generally represent metastatic foci. Only three cases of primary involvement of the skin are present in the literature. Diagnostic recognition of this entity is problematic due to subtle morphological and immunophenotypic features which may easily be overlooked or mistaken for more common entities.
Design: Histological, immunohistochemical and ultrastructural studies were performed on three routinely processed excisional biopsies. A clinical review was also performed.
Results: Histomorphology and immunophenotype were consistent with the diagnosis of Interdigitating dendritic cell sarcoma in all cases. Ultrastructural features were also compatible. S-100, CD68, CD99, and WT-1 immunohistochemical staining were diffuse and strong in a staining pattern that highlighted the interdigitating cellular processes. Two cases were found to represent primary cutaneous disease with no evidence of underlying nodal or visceral disease. The third case was found to represent nodal disease originating from an intraparotid lymph node.
Conclusions: Here, we report only the fourth and fifth cases of a primary cutaneous IDCS as well as an additional case presenting within an intraparotid lymph node that was initially diagnosed as melanoma. IDCS represents an under-recognized and challenging malignant tumour that can easily be misdiagnosed due to overlapping features with more common cutaneous entities. We report for the first time immunohistochemical positivity of this tumour for WT-1 and CD99. Furthermore, WT-1 in particular, demonstrates a distinctive dendritic pattern of staining that can be used as a useful discriminating feature from other cutaneous lesions in the differential diagnosis.
Category: Dermatopathology

Monday, March 22, 2010 2:45 PM

Platform Session: Section F, Monday Afternoon


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