Which markers define the IHC profile of breast myoepithelial cells?

• A. SMA, p63/p40, calponin, SMMHC
• B. ER, PR, HER2
• C. CK7, CK20, GATA3
• D. CD34, GPC3

Answer: (A)

This question hinges on which markers reflect the contractile, basal-like nature of breast myoepithelial cells. Myoepithelial cells wrap around ducts and acini and have a smooth muscle–type, contractile phenotype. To visualize them in tissue, you look for markers that highlight this contractile/basal character: smooth muscle actin (SMA) and calponin indicate actin-based contractile proteins, while smooth muscle myosin heavy chain (SMMHC) reinforces the smooth muscle–type lineage. In addition, p63 and its family member p40 are nuclear transcription factors strongly expressed in myoepithelial (basal) cells, making them reliable markers to identify this cell layer.

Using this combination is especially helpful because it distinguishes the myoepithelial layer from luminal epithelial cells, which matters when evaluating breast lesions for invasion. The other marker groups target luminal epithelial characteristics (ER, PR, HER2), general epithelial cytokeratins and related transcription factors (CK7/CK20, GATA3), or unrelated lineages (CD34, GPC3), and thus do not define the myoepithelial profile.