Which marker is included in the breast myoepithelial cell IHC profile?

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

Answer: (A)

Myoepithelial cells in the breast have a contractile, smooth muscle–like phenotype, so their IHC profile includes markers of smooth muscle and basal/myoepithelial differentiation. Markers such as SMA (smooth muscle actin), calponin, and smooth muscle myosin heavy chain (SMMHC) reflect the contractile nature, while nuclear p63 or p40 highlight basal/myoepithelial cells. Together these markers reliably identify the myoepithelium that surrounds ducts and lobules and help distinguish it from the luminal epithelial layer, which is crucial when evaluating invasion in breast lesions.

ER, PR, and HER2 are hormone and growth receptors used to classify epithelial breast carcinomas, not myoepithelium. CK7, CK20, and GATA3 mark epithelial lineage, with GATA3 commonly expressed in breast epithelium, again not specific for myoepithelium. CD34 and GPC3 are not typical myoepithelial markers; CD34 marks vascular or some stromal cells, and GPC3 is associated with hepatocellular and certain germ cell tumors.