Which panel would most strongly indicate breast origin for metastasis?

• A. GATA 3+, ER/PR/HER2(-/+)
• B. Napsin A +, TTF-1 +
• C. Napsin A +, GATA3 -
• D. GATA3 +, Napsin A-

Answer: (D)

The main idea is using immunohistochemical markers to tell where a metastasis likely came from. GATA3 is a marker frequently expressed in breast carcinomas, while Napsin A (and TTF-1) is associated with lung adenocarcinoma. Seeing GATA3 positivity while Napsin A is negative provides the strongest clue that the tumor originated in breast, because you have a breast-specific signal and no lung signal. Receptor status like ER/PR/HER2 can be variable and is not as definitive for tissue origin, so a panel that pairs a breast-specific marker with the absence of a lung marker gives the clearest direction. Panels showing positive lung markers or negative GATA3 point away from breast origin, while GATA3 positivity with unknown or non-definitive receptor status is less conclusive.