Metastatic breast carcinoma cells typically exhibit positive expression of mammary epithelial differentiation markers (e.g., GATA, Mammaglobin, ER/PR, TRPS1) and negative expression of thyroid follicular cell markers (e.g., Thyroglobulin, TTF-1, PAX-8) (10, 23–29). Here, TTF1 is linked to breast carcinoma.