Differences in GATA3 expression among histological/molecular subtypes and grades in infiltrating breast carcinoma (IBC) are important in the diagnosis of metastatic breast carcinoma.

GATA-binding protein 3 (GATA3) is a sensitive and relatively specific marker in invasive breast carcinomas (IBC). The aim of the present study was to determine GATA3 expression among different histological and surrogate molecular breast carcinoma subtypes. Immunohistochemical staining of ER, PR, Ki67, HER2 and GATA3 was performed in a cohort of 84 consecutive cases of primary IBCs. The association of GATA3 expression with different histological subtypes, grades and surrogate intrinsic molecular subtypes was assessed. The overall positivity of GATA3 across various histological subtypes was 71.43% with no correlation with histological type (p = 0.849). Our study also confirmed that GATA3 exhibits a relatively high sensitivity for IBC (78.57%). GATA3 expression was positively correlated with low histological grades (G1/G2) vs. G3: p = 0.001) with most of G3 (57.89%) cases being negative and with luminal A (72.22%) and B (84.62%) subtypes (p = 0.00001) while most of the triple negative (87.5%) and HER2-overexpressed (66.67%) being negative. Caution must be payed however when dealing with an IBC metastasis of HER2-overexpressed or triple negative molecular subtypes or G3, since in these categories according to the present study, GATA3 is more frequently negative that previously reported and may be useless for diagnosis of tumor origin.