Aims GATA-binding protein 3 (GATA3) is a sensitive and relatively specific marker in breast and urothelial carcinomas. Its diagnostic utility in primary and metastatic breast cancers has been explored and confirmed. However, the relationship between GATA3 expression and different breast carcinoma intrinsic subtypes has not been specifically defined in the literature despite a few reports with a small number of cases. The aim of the current investigation is to clarify GATA3 expression among different histological subtypes and surrogate molecular breast carcinoma subtypes in a large series of cases.

Methods Immunohistochemical staining of GATA3, GCDFP15 and mammaglobin was performed in a cohort of 1637 cases of primary invasive breast carcinoma. The association of GATA3 expression with different histological and surrogate intrinsic subtypes was assessed and compared with the expression of GCDFP15 and mammaglobin.

Results The overall positivity of GATA3 across the various immunohistochemistry-based surrogate intrinsic subtypes was 99.51% for luminal A-like, 97.70% for luminal B-like, 68.50% for HER2 overexpression and 20.16% for triple negative breast cancers. GATA3 expression was positively correlated with estrogen receptor (ER)-positive (luminal subtypes) breast carcinomas. For luminal-like and HER2 overexpression subtypes, GATA3 was much more sensitive than GCDFP15 and mammaglobin. For triple negative tumours, GATA3 was less sensitive than GCDFP15.

Conclusions GATA3 exhibits a relatively high sensitivity for breast carcinomas. It is more sensitive than GCDFP15 and mammaglobin in luminal-like and HER2 overexpression subtypes. GATA3 expression is associated with breast carcinomas of luminal subtype and low histological grade.