Which combination correctly represents the Breast Microinvasion Cocktail markers?

• A. Cytokeratin 5/6 + p63 + Cytokeratin 8/18
• B. Cytokeratin 5/6 + p63
• C. p63 + Cytokeratin 14
• D. Cytokeratin 8/18 only

Answer: (C)

The essential idea is to visualize the myoepithelial layer around ducts to distinguish in situ disease from invasion. A breast microinvasion cocktail should robustly label myoepithelial/basal cells. The combination of p63 and Cytokeratin 14 fits this need: p63 is a strong nuclear marker of myoepithelial cells, and CK14 marks the basal cytokeratin in those same cells, producing a clear, reliable myoepithelial rim around ducts. When this rim is intact, the lesion is more consistent with non-invasive disease; disruption of the myoepithelium suggests invasion. Other options include luminal markers like Cytokeratin 8/18, which would stain the epithelial lining rather than the myoepithelium and thus aren’t appropriate for delineating microinvasion. CK5/6 can mark basal cells too, but CK14 with p63 is a more specific, widely used pairing for this purpose.