Abstract
The prevalence of breast cancer is rising worldwide. The main cause of death from breast cancer is distant metastasis, which occurs within 3 years after diagnosis in 10–15% of patients. The initiation and progression of breast cancer have been related to both external and internal factors, including viral infection. Human cytomegalovirus infection (HCMV) is common in breast cancer and metastases, and high tumor levels of HCMV appear to worsen outcomes. HCMV can increase the malignant behavior of tumor cells by modulating multiple cellular regulatory and signaling pathways and enhance the proliferation, survival, invasion, motility, and adhesion of tumor cells. Although HCMV seems to have an oncomodulatory role in breast cancer, definitive evidence for a causal role is lacking, and further studies are needed. The current review will discuss evidence that links viral infections to breast cancer.
Highlights
mammary tumor virus (MMTV) was linked to human breast cancer approximately 50 years ago [26]
MMTV transcripts were identified in breast cancer samples in some studies but not in others [28,29]
Other studies have shown tumor development in MMTV-cyclin D1 transgenic mice, which emphasizes the importance of cyclin D1 in breast cancer [34,35]
Summary
Breast cancer has been mentioned in almost every period of documented history, beginning with the Egyptians, who described the disease some 3500 years ago [1,2,3,4]. The number of breast cancer cases is increasing worldwide. The World Health Organization reported differences in the incidence of breast cancer worldwide, from 89.7 per 100,000 women in Western Europe to 19.3 per 100,000 women in Eastern Africa [9]. The Swedish Social Board reported that breast cancer was the most common cancer in women, responsible for 30.3% of cases, and that the average annual increase was 1.3% over the preceding two decades [10]. Breast cancers are divided into three subtypes: about 60% are estrogen- or progesterone-positive (ER/PR), 20% have increased expression of the oncogene human epidermal growth factor receptor 2 (HER-2/neu), and 20% are triple-negative, lacking expression of ER, PR, and Her-2/neu [16,17,18,19]. Despite the possible role of this virus in the initiation and progression of breast cancer, definitive evidence for a causal role is lacking
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