Immunohistochemical evaluation of GATA-3 expression in ER-negative breast carcinomas

Objectives: Estrogen receptor (ER), gross cystic disease fluid protein 15 (GCDFP-15), and mammaglobin (MGB) are commonly used breast-specific immunomarkers; however, about half of metastatic breast carcinomas are negative for all three. GATA-binding protein 3 (GATA-3) has emerged recently as a sensitive and relatively specific immunomarker for breast and urothelial carcinomas, but the data documenting its expression in ER-negative breast carcinomas are limited; this often poses a dilemma in the setting of metastases. The purpose of this study is to investigate expression of GATA-3 in ER-negative breast carcinomas. Methods: Immunohistochemical evaluation of GATA-3, GCDFP-15, and MGB on 96 ER-negative breast carcinomas was performed. Results: Overall, 69% (66/96), 15% (14/96), and 35% (34/96) of ER-negative breast carcinomas expressed GATA-3, GCDFP-15, and MGB, respectively. Conclusions: Our data suggest that GATA-3 is, so far, the best breast-specific immunomarker, especially when encountering ER-negative metastatic breast carcinomas. GATA-3 should be included in the panel of immunomarkers in the workup of tumors of unknown primary.