Digital Atlas of Breast Pathology by Meenakshi Singh, MD © - Department of Pathology, Stony Brook University Medical Center

Normal breast, H + E stain.
Each of the lobules is surrounded by myoepithelial cells which stain for high molecular weight cytokeratin, p63, calponin, etc. On this H and E, these cells are seen as spindled cells surrounding the lobules.