Infiltrating immune cells in 30 primary human epithelial breast tumours were studied using specific anti‐CD3 (T cells), anti‐CD68 (macrophages), anti‐CD57 (NK cells), and an anti‐pan‐B cell antibody (L26). The majority of tumour infiltrating inflammatory cell are T cells (40‐50%) and monocytes/macrophages (15–35%).

The macrophage specific chemo‐attractant and growth factor CSF‐1 is detected by immunohistochemical techniques (IHC) at the level of invasive breast cancer cell in 46/50 tumours but not at the level of in‐ situ (pre‐invasive) cancer. A mosaic staining patterns was usually observed with a very high expression in areas of obvious stromal invasion (90%cells positive) and absent or trace staining in intraductal carcinoma. Macrophages and plasma cell are equally intensely positive. In‐situ‐hybridisation experiment confirm the production of CSF‐1 (mRNA) by tumour cells and show the same pattern of expression. Expression of the CSF‐1 receptor protein (fms) was also observed by IHC in 41/48 invasive tumours, albeit at weaker intensities than in tumour infiltrating monocytes/macrophages. A concomitant expression of both CSF‐1 and fms in in‐situ carcinoma was never seen (n = 14). It is therefore proposed that the associated expression of CSF‐1 and its receptor may be linked to the invasive potential of breast cancer, the monocytic infiltrate being an indication of the quantitative importance of CSF‐1 production by the tumour. © 1992 Wiley‐Liss, Inc.