A myoepithelial cell that surrounds milk-secreting luminal epithelial cells. This cell type contracts under the stimulation of oxytocin and is attached to the basement membrane by hemidesmosomes and to the adjacent luminal cells by desmosomes. This cell type expresses high level of keratin-14 and is estrogen receptor alpha negative. [ GOC:tfm http://www.ncbi.nlm.nih.gov/pubmed/11250738 http://www.ncbi.nlm.nih.gov/pubmed/19022771 ]