In a patient with a history of breast cancer, which panel would be most valuable to determine the diagnosis of mediastinal lymph node cells?

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

Answer: (C)

Determining tissue origin for metastatic lymph node cells relies on lineage-specific markers. GATA3 is a strong indicator of breast (and urothelial) origin, while the ER/PR/HER2 receptor status provides breast-specific phenotype information. In contrast, Napsin A and TTF-1 point toward a lung primary if they are positive.

In a patient with a history of breast cancer, a panel that shows GATA3 positivity along with the breast-related receptor profile (ER and/or PR and/or HER2) is the most informative because it directly supports metastatic breast carcinoma and helps distinguish it from a new primary lung cancer. Napsin A or TTF-1 positivity would suggest lung origin, which is less consistent with the history unless proven otherwise.

So, the panel combining GATA3 positivity with ER/PR/HER2 status best identifies metastatic breast cancer in mediastinal lymph node cells.