Human cytomegalovirus (HCMV) is a common human pathogen infecting more than 70% of the world’s population. The virus has developed mechanisms to evade the host’s immune systems and it usually remains latent in its host. The expressed HCMV proteins have the potential to interfere with cell metabolism and promote the development of tumors. The detection rate of HCMV is relatively high in both non­neoplastic and neoplastic breast epithelium in patients with breast cancer. Meanwhile, published studies indicate that exposure to the virus in later development stages can cause breast cancer. Recent progress on new anti­HCMV targeted therapy for breast cancer also indicates that HCMV is likely involved in the progression of breast cancer. In this review, we will discuss the oncogenic potential of HCMV and the potential association of HCMV with the initiation and progression of breast cancer.