Background: Intraductal breast fluids containing exfoliated mammary epithelial cells can be harvested from the breast by ductal lavage to screen for disease-associated cytologic abnormalities. In addition to epithelial cells, breast fluids contain large numbers of mammary foam cells, and the tissue of origin of these foam cells has been the subject of controversy for many years. Immunocytochemical, morphologic, and molecular studies variously have supported a mammary epithelial origin versus a histiocytic origin for this cell type. In the current study, the authors performed immunocytochemical analysis with epithelial specific and macrophage specific antibodies to characterize and quantify breast cells obtained by ductal lavage.
Methods: Breast fluids were harvested from 19 individual breast ducts in 15 female patients by ductal lavage. Cells from each specimen were processed for immunocytochemical staining using the AE1/AE3 multicytokeratin and CD68 (clone KP1) monoclonal antibodies. Cells were classified as mammary epithelial cells or mammary foam cells on the basis of morphologic criteria, and the cells were counted and evaluated for immunoreactivity with epithelial specific and macrophage specific antibodies.
Results: The CD68 macrophage specific antibody stained all ductal lavage cells that exhibited foam cell morphology. The AE1/AE3 multicytokeratin antibody demonstrated strong, positive staining of cells that exhibited epithelial morphology but failed to demonstrate significant staining of mammary foam cells. The lavage specimens contained a range of 3040-278,850 epithelial cells and 2230-90,480 foam cells. The median numbers of epithelial cells and foam cells per lavage sample were 15,680 and 29,200, respectively. The ratio of epithelial cells to foam cells varied among specimens ranging from 3.4 to 0.09 (median, 0.8). Seven of 19 lavage specimens contained more epithelial cells than foam cells, whereas 12 samples contained a greater proportion of foam cells.
Conclusions: Immunocytochemical analysis using the AE1/AE3 multicytokeratin and CD68 antibodies supports a histiocytic origin for the majority of mammary foam cells harvested from the ductal system of the human breast by ductal lavage. Although mammary foam cells constitute a significant proportion of the cellular population obtained by ductal lavage, thousands of epithelial cells also are harvested.