Abstract

Inflammatory malignant fibrous histiocytoma (IMFH), consisting of large, atypical histiocyte-like cells set amidst an inflammatory backdrop of eosinophils, neutrophils, lymphocytes, and xanthoma cells, can be difficult to distinguish from Hodgkin's disease and non-Hodgkin's lymphoma, particularly of the Ki-1 anaplastic large-cell type in small biopsy specimens. This problem is becoming more prevalent with the use of needle biopsies guided by computed tomography for definitive diagnosis. For this reason, we studied the expression of a battery of leukocyte markers in IMFH to evaluate whether they could serve as an independently reliable means of distinguishing amongst the three neoplasms. Eight examples of histologically typical IMFH were stained with a number of leukocyte markers that included CD30 (BerH2), CD15 (leuM1), CD45/ CD45RB (2B11,PD7/26/16), CD43 (leu 22), CD45RO (A6), CD20 (L26), and CD68 (KPI). The large anaplastic tumor cells within IMFH consistently lacked CD30, CD15, CD45/CD45RB, CD43, CD45RO, and CD20. In one case, the anaplastic cells expressed CD68. Benign histiocytes within IMFH expressed CD68 and displayed variable expression of CD15, CD45/CD45RB, and CD43. The reactive lymphocytes consisted mostly of scattered small T cells with a few B cells, mainly within lymphoid aggregates. We conclude that the immunophenotypic profile of the anaplastic cells in IMFH (lack of CD15, CD30, CD43, CD45/CD45RB, CD45RO, CD20) differs from most cases of Hodgkin's disease (ICD30+, CD15+/-) and from Ki-1 anaplastic large cell lymphoma (CD30+, CD45/CD45RB+/-, CD43+/-, CD45RO+/-, CD20-/+). Immunohistochemistry is an important diagnostic adjunct, provided care is taken to exclude benign histiocytes and inflammatory cells from consideration.