Basal clear cells of the normal human breast.

The ductal system of the human breast consists of two major cell types: epithelial and myoepithelial. In some reports a third cell type, given various names is mentioned. In this study it is called a basal clear cell. The role of this cell, unlike that of the epithelial and myoepithelial cells, remains unclear, although it has been suggested that it may have a stem cell function. We illustrate here that there is an ultrastructural transition between the basal clear and myoepithelial cell; suggesting that it acts as a precursor of the myoepithelial cell, and may not be a stem cell for both epithelial and myoepithelial cells.