KP-1 (CD68) is a recently described
monoclonal antibody to a cytoplasmic
epitope present on tissue histiocytes and macrophages. To determine the specificity and sensitivity of this marker in the evaluation of cases of
malignant fibrous histiocytoma (MFH), this
reagent and a panel of commercially
antibodies were used to
stain formalin-fixed
paraffin sections from 25 cases of MFH and 25 other
tumors, including a variety of
soft-tissue sarcomas. Eighteen of 25 cases of MFH stained for KP-1 (72%), whereas all other
tumors were negative, including 12 cases of pleomorphic
soft-tissue sarcoma other than MFH. The percentage of
tumor cells staining for KP-1 varied. In 11 cases KP-1 was only focally present, but staining was of a high intensity and associated with minimal nonspecific or background staining. Pleomorphic histiocytic cells and spindle cells from storiform
tumors were strongly decorated with
antibodies to KP-1 in most cases, and
antigen also was present on
tumor giant cells. Although alpha-1-antitrypsin and alpha-1-chymotrypsin stained a higher percentage of cases of MFH (92%), immunoreactivity for these markers also was noted in other
tumors. Because of its specificity as a histiocyte marker, KP-1 is a useful component in a panel of
antibodies for the characterization of
soft-tissue sarcomas and the diagnosis of MFH.