This book was designed as case-control study and performed in the period between October 2016 to June 2017 in Central public health laboratory, Baghdad, Iraq. It includes samples from 90 women; 60 breast cancer patients, 20 benign tumor patients, and 10 normal breast tissues as a control group. A blood sample and formalin-fixed paraffin embedded tissue block with histopathological report were obtained by a pathologist from each woman included in this study, according to ethical approval. The practical part of this study was designed around two main pathways. First, serological detection of anti-HCMV IgG and IgM was performed using the ELISA technique. Second, Immunohistochemically technique to demonstrate the expression of HCMV early and late antigens as well as HER2 expression in malignant, benign and normal breast tissues. These findings are the first to demonstrate the correlation between Human cytomegalovirus early and late antigens with Her2/neu overexpression in breast cancer.