OBJECTIVETo study the morphologic features, immunophenotypes, differential diagnoses and prognosis of histiocytic sarcoma (HS).

METHODSThe clinical and pathologic findings of 6 cases of HS were reviewed. Immunohistochemical assay (Elivision staining) was also performed. Follow-up information was available in 4 patients.

RESULTSThere were altogether 3 males and 3 females. The age of patients ranged from 12 to 81 years old (median = 54.6 years). The sites of involvement included lymph node (number = 2 cases) and skin or soft tissue (number = 4 cases). The tumor was composed of sheets of large epithelioid cells with abundant eosinophilic cytoplasm, oval to irregular nuclei, vesicular chromatin and large nucleoli. Binucleated form was not uncommon. Two of the cases showed increased pleomorphism with multinucleated tumor giant cell formation. Focal cytoplasmic with foamy appearance was identified in 3 cases. One case demonstrated foci of spindly sarcomatoid appearance. Hemophagocytosis was identified in 2 cases. Mitotic figures were readily identified. The tumor cells were often accompanied by various numbers of inflammatory cells. Immunohistochemical study showed that all cases were diffusely positive for leukocyte common antigen, CD4, CD68 and CD163. Four of the 5 cases studied also expressed lysozyme. Amongst the 4 patients with follow-up information available, 3 died of the disease at 6 to 11 months interval after diagnosis. One patient, whose lesion was localized at the skin and soft tissue, survived for 3 years, with no evidence of tumor recurrence.

CONCLUSIONSAccurate diagnosis of the HS is based on the combination of morphologic examination and immunohistochemical assay. HS often presents with clinically advanced disease and pursues an aggressive clinical course, with a poor response to therapy. However, a subset of cases presenting with clinically localized lesion may carry a relatively favorable long-term outcome.