Immunohistochemical characterization of histiocytic tumours

Immunohistochemical labelling of histiocytic tumour cells in formalin-fixed paraffin-embedded material was usefully applied to malignant fibrous histiocytoma (MFH) and to malignant histiocytosis (MH). Not all cases of MFH showed a positive reaction, in contrast with the obligatory positive staining in MH. In general, histiocytic tumour cells stained more intensively with alpha 1-antichymotrypsin than with lysozyme. False positive results can be due to intermingled non-neoplastic histiocytes or degenerating neoplastic cells in any mesenchymal tumour.