Malignant histiocytic neoplasms of the small intestine.

Immunologic studies have demonstrated that the vast majority of hematolymphoid neoplasms previously designated as "histiocytic" are lymphoid in origin. Consequently, malignancies of macrophage lineage are considered rare by most authors; indeed, their existence is doubted by some. Herein we report two cases of malignant histiocytic neoplasms (malignancies of macrophage lineage) of the small intestine. Both patients presented in the 7th decade with symptoms related to an abdominal mass. The polypoid tumors protruded into the intestinal lumen, extended through the entire thickness of the bowel wall, and involved regional lymph nodes. Microscopically, sheets of large pleomorphic histiocytic cells infiltrated around crypts and were associated with an admixture of bizarre giant cells and inflammatory cells. Mitotic figures were easily found. Ultrastructurally, the cells lacked desmosomes and had indented or kidney-shaped nuclei and cytoplasm containing mostly lysosomes and dense lipid droplets. In both cases, paraffin section immunohistochemistry revealed reactivity of tumor cells for CD45RB (LCA), CD45RO (A6), CD68 (KP1), CD15 (LeuM1), and lysozyme. Frozen section immunohistochemistry performed in one case further supported the macrophage phenotype. Southern blot studies of this case did not reveal immunoglobulin or T-cell receptor beta chain gene rearrangements. One patient initially treated by surgery only died of disease 3 years after diagnosis. The second patient is alive and disease-free 2 years following postoperative combination chemotherapy. The diagnosis of malignant histiocytic neoplasms requires the use of a panel of immunohistochemical markers and may be supported by electron-microscopic studies.