Biochemical and ultrastructural features of human milk and nipple aspirate fluids.

Breast duct epithelium produces, secretes, and metabolises several biologically important compounds, which are found in breast secretions obtained in physiologic and pathologic conditions (milk and nipple aspirate fluids, respectively). In order to preliminarily evaluate the ultrastructural morphology of the cells found in Type II nipple aspirate fluids (NAF) and correlate it with the biochemical profile of the extracellular fluid present in these breast secretions and in human milk, we analyzed 72 NAFs from nonlactating premenopausal women affected by various breast diseases and 10 normal milk samples. Although several constitutive proteins were detected in all samples examined, the preliminary biochemical analyses and electrophoretic profiles revealed characteristic behaviours for several biologic constituents, suggesting a possible basic mechanism of production by breast epithelial cells during both physiologic and pathologic conditions. The ultrastructural analysis of milk cellular components give preliminary evidence of the apocrine secretion mechanism peculiar of breast gland, whereas Type II NAF cells appeared as biosynthetically active cells, showing a possible modified secretion mechanism. Our multidisciplinary approach seems to support the hypothesis that cellular and biochemical behaviour of Type II NAF may be an useful tool to identify aberrated breast epithelial cells in nonlactating women that might be prone to premalignant transformation.