GATA3 binding protein 3 or GATA3, is a zinc finger transcription factor important in cell proliferation, development, and differentiation. The human GATA3 gene has been mapped to chromosome 10p15. GATA3 is mostly observed in breast and urothelial carcinomas, and rarely present in other cancers such as endometrial endometrioid adenocarcinoma. Among the breast carcinomas, GATA3 has a lower expression in luminal B subtype breast carcinoma. Studies have found GATA3 expression to be associated with ER (estrogen receptor), PR (progesterone receptor), and Her2 in breast cancer cases. Urothelial carcinomas stain positively for GATA3 in invasive or high grade tumors. Anti-GATA3 can also be useful in the identification of unknown primary carcinoma when carcinomas of the breast or bladder are a possibility