IHC stains:
Diagnosis: Histiocytic Sarcoma
Histiocytic sarcoma (HS) is a rare malignancy with morphological and immunophenotypic characteristics of mature tissue histiocytes. Neoplastic proliferation associated with acute monocytic leukemia should be excluded.
Etiology is not known. Subset cases are associated with mediastinal germ cell tumor. It occurs mainly in adults (mean age of 52yo), but has wide age range (from infancy to elderly. It commonly involves extranodal sites, GI, skin, soft tissue, etc.
Morphology: large cells with abundant eosinophilic cytoplasm, cytoplasmic vacuoles, monomorphic or pleomorphic, mixed inflammatory cells, multinucleated giant cells.
Immunophenotype: positive for CD68, CD4, CD163, lysozyme, CD43, CD45; negative for CD21, CD35, CD1a, CD207, CD13, CD33, MPO, B-cell or other T-cell markers.
The differential diagnosis of HS includes DLBCL, inflammatory pseudotumor, follicular dendritic cell sarcoma, interdigitating dendritic cell sarcoma, Langerhan cell sarcoma, large cell anaplastic lymphoma, melanoma and other sarcomas. The prognosis of histiocytic sarcoma is poor.