A 68 year old woman underwent an excisional biopsy because of architectural distortion.
Diagnosis: Sclerosing adenosis with prominent myoid component.
Discussion: The normal lobular unit is composed of luminal and myoepithelial cells (MEC), the latter containing microfilaments, cell matrix adherens junctions and smooth muscle specific cytoskeletal proteins. MECs are true epithelial cells, however, because the major components of their intermediate filament system are cytokeratins 5 and 14, because they form desmosomes, hemidesmosomes, and cadherin-mediated cell-cell junctions, and because they are permanently separated from the connective tissue by underlying basement membrane. (Deugnier, M-A, et al. The importance of being a myoepithelial cell. Breast Cancer Research 2002, 4:224).
Myoepithelial cells may show prominent myoid component, sometimes referred to as myoid hypertrophy, and this phenomenon can cause dramatic atrophy of the luminal component (so-called myoid atrophy). This finding is of no clinical significance, but makes for pleasing microscopic images.