Viruses cause some breast cancers.

docs.google.com/viewer

8. Conclusions 

Breast cancer is one of the most frequently diagnosed malignancies of women in many populations. Previous studies provide evidence that viruses exist in patients with breast cancer and suggest viruses can be one of the risk factors for breast cancer [97,98]. Several candidate viruses such as the specific Cancers 2010, 2 506 

types of HPV, EBV, HCMV, HHV-8, MMTV and HERV have been proposed. However, some of these studies are disputed. The identification of a MMTV strengthens the possibility of the viral etiology for breast tumors in animals. Although it has been assumed MMTV might be involved in the pathogenesis of human breast cancer, similar viral sequences found in humans cannot provide direct evidence of carcinogenesis. The presence of high-risk HPV, EBV and HHV-8 has been detected in breast cancer specimens, but the association of these candidate viruses with breast cancer has shown inconsistent results in different studies. A more specific approach, such as combining real-time quantitative PCR (to measure the amount of viral load in archival tissue samples) with laser capture microdissection (to improve localization of viral nucleic acid in benign or malignant components of a tissue sample) is suggested for further investigation [73]. Moreover, the possibility of multiple viral factors being involved in breast cancer has also been reported [20,44]. By PCR and Southern hybridization analysis of HSV-1, HPV, HCMV, EBV, and HHV-8 DNA in some of the tissues of patients with breast cancer and non-breast cancer controls, it was found the presence of multiple viruses was not detected in the non-cancerous and thyroid tumor groups, but was common in the breast cancer and fibroadenoma groups [20]. The presence of more than one virus was found predominantly in breast cancer, suggesting multiple viral factors may be associated with breast cancer. If an association between one, or more, of these viruses and breast cancer is verified, it may help develop new anti-viral therapies and vaccine strategies for combating this increasingly common cancer. More efforts are needed to provide conclusive evidence linking viruses to the etiology of breast cancer.