Background: Breast carcinoma is a major public health problem. Claudins are important tight 
junction proteins, they came into focus for their suggested role in carcinogenesis and possible role in 
cancer therapy. To date, few studies have addressed the role of claudins in BC. Claudin-4 has been 
found to be overexpressed in a wide variety of cancers including breast cancer, its role in BC 
progression and spread constitutes an active research focus. Methods: Immunohistochemical staining 
of claudin-4 was conducted on 50 tissue specimens of invasive ductal carcinoma of the breast (IDCNST) by using the avidin biotin-peroxidase complex method with diaminobenizidine (DAB) 
chromagen detection system. Results: High claudin-4 expression was detected in 52% of cases. 
Claudin-4 expression showed statistically significant association with tumor laterality, tumor grade, 
stage, advanced nodal status, LNR, NPI, Ki67 PI, ER& PR status and triple negative phenotype (p.= 
0.008, 0.027, 0.016, 0.043, 0.006, 0.006, <0.001, 0.014, 0.019 and 0.047 respectively). On comparing 
claudin-4 expression in 12 pairs of primary IDC-NST and their corresponding LN metastasis, a 
concordance rate of 75% was found between primary tumors and their metastatic LNs where 9/12 
cases maintained the same expression score. Conclusions: Claudin-4 expression is suggested to be a 
molecular protein with an oncogenic function and biological value. Being involved in IDC-NST 
progression and its association with many poor prognostic factors of IDC-NST, the important role in 
progression and spread in invasive ductal breast carcinoma is highlighted.