Despite the evidence indicating the presence of viral proteins and DNA in breast tumor tissue, HCMV is not typically considered an oncogenic virus . Virus infection can, however, promote many of the classic hallmarks of cancer [21, 22], such as cell cycle dysregulation, inhibition of apoptosis, increased migration and invasion, and immune evasion [20, 23]. HCMV has been linked not only to breast cancer, but to an array of other malignancies, including glioblastoma [24–27], medulloblastoma , colon cancer , and prostate cancer . Individual HCMV gene products can have profound effects on cell growth, such as immediate early proteins IE1 and IE2, which are known to stimulate entry into S phase [31, 32]. IE1 expression was found to increase the growth rate of glioblastoma cells in culture, suppress p53 and Rb tumor suppressor activity, and stimulate PI3K/Akt signaling . IE1 was detected in breast tumor tissue [10, 11] as well as in CD133+ glioma stem cells isolated from glioblastoma multiforme (GBM) patients , suggesting that IE1 may promote tumorigenesis enhancing the growth and self-renewal of tumor stem cells.