Histiocytic sarcoma in the small intestine: a case report with flow cytometry study and review of the literature.

We describe a case of true histiocytic sarcoma (HS) with features of HS in clinical manifestation, histological presentation, and immunohistochemical panels. The flow cytometry studies were used for the diagnosis. The tumor presents in the small intestine with involvement of regional mesenteric lymph nodes of a 68-year-old female. Histological examination reveals that tumor cells are large and pleomorphic. They have vesicular chromatin and abundant eosinophilic cytoplasm. Immunohistochemical studies show the tumor cells to be positive for CD45 (LCA), CD45RO, CD4, CD68, and lysozyme; and negative for all other T-, B-, macrophage, follicular dendritic- and hematopoietic-cell markers. Proliferation rate is 5% by MIB stain. Flow cytometry studies reveal large atypical cells positive for CD4, CD14, and CD45. There are 29 cases of HS reported in the literature since 2001. All of these cases are summarized. The diagnostic methods and the possible prognostic factors are discussed. We believe that the correct diagnosis of HS is important for clinical treatment and prognostic prediction, although it is very rare.