Breast cancer (BC) is one of the most common cancers in the world. In numerous tissues, including the breast, GATA3 plays an important role in stimulating proliferation and differentiation. The main aims of this study is determining the types of BC (IDC and ILC) then the estimation of the role of GATA3 protein expression by immunohistochemical staining method (IHC) in BC patients and control groups as a biomarker.

The present study was done during the period from October 2020 to April 2021. Sixty seven tissue samples block embedded in wax taken from BC female patients and thirty four of normal non-tumoral breast tissue as a control group collected randomly with their data from three private pathological clinics, these blocks have been prepared between (2014 – 2021), three pathologists re-evaluate each pathologic material.

Regarding to IHC GATA3 protein expression, after histological re-evaluation of slides, the rate of IDC was 80.6% (54 patients) and of ILC was (19.4%) (13 patients).The scoring system +1 (37.3%) and +2(19.4%) increased significantly in BC patients than control (P=0.001), in addition to, the nuclear positive expression of GATA3 decrease significantly in BC patients than control (Odd ratio 2.55, 95% CI 1.45-2.37, P=0.0001), On the other hand, the positivity of GATA3 protein increased significantly in patients with invasive ductal carcinoma (IDC) (P=0.001).

Keyword: GATA3, Breast Cancer, Immunohistochemical Expression.