This proposal aimed to examine the role of a tumorigenic virus, Epstein-Barr virus (EBV), in etiology of breast cancer. EBV is an almost ubiquitous human herpesvirus that establishes lifetime latent infections in humans. It was the first human tumor virus discovered through its association with Burkitt's lymphoma in Africa. EBV infection also associates with various malignancies and proliferative syndromes, mainly affecting lymphoid and epithelial tissues. In lymphoid tissues these include Burkitt's Lymphoma, Hodgkin's disease, some adult T-cell lymphomas, and immunoblastic lymphoma in patients with immune dysfunction. EBV associates with the epithelial pathologies nasopharyngeal carcinoma and oral hairy leukoplakia. Recent studies have also found the EBV genome and viral gene expression in breast cancers using a variety of sensitive detection techniques. In the current proposal for the Department of Defense, we investigated the mechanism of EBV infection of breast epithelial cells.