OBJECTIVETo investigate the clinicopathologic features, immunophenotyping, differential diagnoses and prognosis of histiocytic sarcoma (HS).

METHODSThe clinical and pathologic findings of 4 cases of HS were reviewed. The samples were used for paraffin section, HE stain, immunohistochemistry stain by EnVision method, electron microscope observation. Follow-up information was available in all patients.

RESULTSThe age of patients, 2 males and 2 females, ranged from 22 to 65 years old (median, 43.25 years). The sites of involvement included lymph node (2 cases), skin or soft tissue (1 case) and colon (1 case). The tumor cells were widespread infiltration, diffused distribution, no adhesion to each other. Tumor cells were middling and large, round, orbicular-ovate, polygon, epithelium appearance, plentiful cytoplasm and acidophilia, cystose. Nucelus was round, orbicular-ovate, dissymmetry. Nuclear chromatin was vacuole appearance, basophilia nucleolus, caryocinesia and pathological mitotic figure. Three of the cases showed conjugate nuclei, increased pleomorphism with multinucleated tumor giant cell formation. Focal cytoplasmic with foamy appearance was identified in 2 cases. One case demonstrated foci of spindly sarcomatoid appearance. Hemophagocytosis was identified in 2 cases. The tumor cells of 4 cases were often accompanied by various numbers of inflammatory cells. Immunohistochemical study showed that all cases were diffusely positive for α-1-ACT, CD68, CDl63 and lysozyme. Three of 4 cases also expressed CD45, CD45RO. The electron microscope results of 4 cases showed that the tumor cells were plentiful cytoplasm and a few cytolysosome in the cytoplasm, and no birbeck cytorrhyctes, cell-cell junction and digitation. Amongst the 4 patients with follow-up information available, three died of the disease 6-13 months after diagnosis. One patient, whose lesion was localized at the skin and soft tissue, survived at the present time.

CONCLUSIONHS was a scarce malignant tumor with mature histiocyte morphology and immunophenotype character. The diagnosis should be based on tissue morphology, immunohistochemistry and electron microscope observation to exclude other disorders.