Does mouse mammary tumor-like virus cause human breast cancer? Applying Bradford Hill criteria postulates

The role of mouse mammary tumor-like virus (MMTV-like virus) in human breast cancer (BC) has already been widely investigated worldwide with conflicting results. Although the researchers tried to establish the link between MMTV-like virus and BC through the statistical meta-analysis of the previous studies associating MMTV-like virus with BC, they failed to establish a more reliable link due to the shortcomings of the statistical meta-analysis. In the present study, we identified population-wide studies relating MMTV-like virus with BC through the PubMed search engine. Then, we examined the available data of MMTV-like virus prevalence in BC, normal/benign samples, and applied the postulates of Bradford Hill criteria on the available evidence to investigate the association between MMTV-like virus and BC. In addition, to further enhance the reliability of our outcomes, we have also evaluated the methodologies of the previous studies to address the possibility of false-negative and false-positive results. After a careful evaluation of the extracted data against the postulates of Bradford Hill criteria, it was observed that none of the studies fulfill all the major postulates of Bradford Hill criteria for causation including temporality, consistency, biological gradient, experiment, coherence, specificity, and analogy. Hence, no causal relationship has been suggested between MMTV-like virus and BC patients of the any included population. The results failed to prove the causal relationship between MMTV-like virus and BC rather suggested it as a co-participant in the pathogenesis of BC.