GATA binding protein 3 (GATA3) is a zinc finger transcription factor that regulates the development in a variety of tissues and cell types. It has been detected in trophoblasts, epidermis, mammary and salivary glands, urothelia, distal nephron and subsets of T-lymphocytes.

GATA3 has been widely investigated as a marker for breast and urothelial carcinomas. GATA3 expression was detected in the majority of primary (90%) and metastatic (87%) mammary carcinomas. Positivity in triple-negative tumors is reported lower (43-67%). GATA3 is also considered a sensitive marker in the differential diagnosis of urothelial carcinoma from prostate adenocarcinoma, labeling the majority of urothelial carcinomas (86%) and none of prostate adenocarcinoma. It also demonstrates superior sensitivity compared to other urothelial markers: Thrombomodulin and Uroplakin III.

In a large scale analysis of 2,500 tumors, GATA3 was also detected in various epithelial and mesenchymal tumors. This marker is a sensitive but not completely specific for mammary and urothelial carcinomas.