Abstract
This article is a literature review of research that explored the association of bovine leukemia virus (BLV) infection in humans with breast cancer. It summarizes and evaluates these publications. This review does not provide absolute proof that BLV is a cause of breast cancer, but, based on well-respected epidemiologic criteria for causation, it does suggest that BLV infection could be a breast cancer risk factor. Any expansion of the current understanding of breast cancer risk factors may increase possibilities to implement primary prevention strategies. The environmental role that BLV-infected cattle may play as a reservoir for infectious BLV offers possibilities for reducing or eliminating potential transmission of BLV from cattle to humans, and/or eliminating the reservoir.