Mouse mammary tumor virus-like virus infection and the risk of human breast cancer: a meta-analysis

Despite a large number of molecular epidemiological studies, the association of Mouse Mammary Tumor Virus-Like Virus (MMTV-LV) infection with the risk of human breast cancer remains inconclusive mainly due to the heterogeneity in populations involved. We performed a systematic search of multiple bibliographic databases, up to October 2013, to identify all studies on detection of MMTV-LV DNA in human breast cancer using polymerase chain reaction (PCR) and conducted the first comprehensive meta-analysis of published literature to explore the relevance of MMTV-LV to human breast cancer. As a result, meta-analysis of twelve case-control studies identified from the systematic search revealed a significantly increased risk for breast cancer development after MMTV-LV infection (OR=15.20; 95% CI: 9.98-23.13). However, there was no significant correlation between MMTV-LV infection and the transformation from ductal carcinoma in situ to invasive ductal carcinoma (OR=1.16; 95% CI: 0.27-4.97). In addition, MMTV-LV infection was not associated with the expression of estrogen receptor (ER) (OR=0.89; 95% CI: 0.48-1.65), progesterone receptor (PR) (OR=0.73; 95% CI: 0.22-2.42), HER-2 (OR=0.65; 95% CI: 0.30-1.43) or p53 (OR=1.47; 95% CI: 0.79-2.73). Finally, we found that the prevalence of MMTV-LV in breast carcinoma was significantly higher in patients from Western countries (prevalence=40.4%, 95% CI: 28.9%-51.9%) than in Asian patients (prevalence: 8.5%; 95% CI: -7.1%-24.1%) in a subgroup and meta-regression analysis (p=0.015). In summary, the meta-analysis of published studies revealed a significantly increased risk for breast cancer development after MMTV-LV infection. In addition, the prevalence of MMTV-LV is much higher in breast cancer patients from Western countries than Asian patients.