Ultrastructural characterisation of the proliferative (stem?) cells within the parenchyma of the normal "resting" breast.

In this study the proliferative (stem?) cells within the parenchyma of the normal "resting" breast were characterised by the ultrastructural examination of 60 mitotic cells. The parenchyma consists of epithelial and myoepithelial cells plus a few intraepithelial lymphocytes and macrophages. The majority of mitotic cells were randomly distributed throughout the lobules with a few present in ducts. In all cases the cells were identified as luminally positioned polarised epithelial cells. The proliferating cells had similar cytoplasmic features and were indistinguishable from adjacent interphase epithelial cells. No evidence was found for the division of subluminal epithelial or myoepithelial cells. These observations would be consistent with a single cell type giving rise to both epithelial and myoepithelial cells.