Breast cancer is estimated to be the most common malignancy affecting women in Iraq. The cancer antigen CA 15-3 has been used as a possible serum marker of occult and recurrent breast carcinoma, either alone or in combination with other tumor markers such as HER2/neu, that has evolved as a major classifier of invasive breast cancer and target of therapy for the disease. ELISA, used to evaluate serum levels of CA15-3 and immuno-histochemistry staining technique, was used to establish the HER2/neu status. The results of this study indicate an increased level of CA15-3 in breast cancer patients (29.02+/-1.79 IU/ml) as compared to both women with benign tumor and healthy controls (13.78+/-1.24 and 8.92+/-0.48 IU/ml, respectively), and that this increase is associated to advanced stages. Patients with HER2/neu positive malignancies show elevated serum CA15-3 (37.09+/-2.55 IU/ml), as well as patients who developed recurrence (40.75+/-2.11 IU/ml). Our data study suggests that higher levels of CA 15-3 would be a reliable prognostic marker as they were directly related to advanced stages and recurrence. In addition persistent elevation of CA 15-3 was associated to HER2/neu positivity in breast cancer patients.