Carbonic anhydrase IX (CAIX) is an enzyme whose expression is very limited in normal tissues and it is highly expressed in various cancers. Therefore, inhibition of CAIX is considered as a promising therapeutic target for the treatment of solid tumors where hypoxic environment has developed. The aim of the current work is to evaluate the immunohistochemical (IHC) expression of CAIX in breast cancer (BC) of Egyptian patients and to investigate the associations of CAIX expression with the standard clinicopathologic features, IHC subtypes of BC, and overall survival. This retrospective study was conducted on 56 archival cases of Egyptian BC patients. Fifty-one of 56 cases (91. 1%) showed positive expression of CAIX with cytoplasmic localization, whereas 5 cases (8 VSports手机版. 9%) showed negative expression. CAIX IHC overexpression is significantly associated with advanced stage and presence of coagulative tumor cell necrosis (P=0. 03 and 0. 02, respectively). Multivariate analysis revealed Ki67 labeling index and CAIX H-score grouping (P=0. 03 and 0. 02, respectively) as independent prognostic factors affecting BC patients' overall survival. We concluded that CAIX could play a role in the progression of the studied BC cases. CAIX is a good candidate for target therapy. .