We describe a quantitative histological study of 34 breast biopsies using a marker for human macrophages, the monoclonal antibody EBM/11. Seventeen of the biopsies were of malignant tumours. Both benign and malignant breast tissue contained large numbers of macrophages with significantly higher numbers occurring in the malignant group. An analysis was made of macrophage counts according to stage, grade and prognostic index of the malignant tumours. There was no correlation between macrophage numbers and any of these parameters in malignant breast tumours. We discuss the possible reasons why some earlier studies (using other markers such as lysozyme), have shown an apparently insignificant number of intratumoral macrophages. Images Figure 1 Figure 2

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Using a panel of monoclonal antibodies against a variety of lymphoid and non-lymphoid antigens the immunohistological staining pattern of giant cells from a case of giant-cell tumour of bone has been compared with that of osteoclasts from the developing ends of fetal long bones. Only EBM-11, an antibody reacting with a wide spectrum of macrophages, stained both osteoclasts and giant cells; stromal cells and osteoblasts did not react. This indicates that osteoclasts and giant cells are phenotypically and presumably functionally similar. It is argued that the osteoclasts and the tumour-derived giant cells in bone are derived from a similar mononuclear precursor.