Which markers comprise the IHC panel for primary breast adenocarcinoma?

• A. ER/PR, HER2/neu
• B. ER/PR, HER2/neu, GATA3, GCDFD-15, CK7, Mammaglobin, NYBR1
• C. GATA3, GCDFD-15, CK7
• D. Mammaglobin, NYBR1, CK20

Answer: (B)

A robust approach to identifying a breast origin and guiding therapy rests on combining hormone receptor status with lineage-specific markers. ER and PR statuses tell you whether the tumor may respond to hormonal therapy, and HER2 status guides HER2-targeted treatment. To confirm breast lineage, you add markers that are commonly expressed in breast tissue. GATA3 is a transcription factor frequently positive in breast carcinomas, increasing confidence in a breast origin. GCDFD-15 (BRST-2) supports breast differentiation, and CK7 is a cytokeratin typically seen in breast epithelium. Mammaglobin and NYBR1 are breast-specific markers that add even more specificity. Together, this panel provides both clinically actionable receptor information and strong evidence of breast origin.

Other panels either omit important breast-specific markers or include CK20, which is more associated with non-breast primaries (like colorectal or urothelial cancers) and can reduce diagnostic specificity.