The study analyzes the potential link between bovine leukemia virus (BLV), an oncogenic retrovirus in cattle, and human breast cancer. BLV infects lymphocytes in cattle, causing persistent infections; while most animals are asymptomatic, some develop lymphosarcoma. The detection of BLV proviral DNA in milk and meat, along with antibodies and proviral DNA in humans, suggests possible zoonotic transmission. In controlled conditions, human mammary epithelial cells (MCF-10 A) were infected with BLV, and the effect of 17-β estradiol (E2) was assessed as a model for natural exposure. BLV integrated its DNA into human cells, increasing the proviral load in the presence of E2, suggesting E2 enhances viral integration. The virus replicated and produced infectious particles capable of infecting bovine mammary cells (MAC-T). Findings suggest BLV could establish infections in human mammary cells under certain conditions, potentially contributing to cancer development. The study highlights the need for further research into its zoonotic potential and emphasizes the importance of food safety practices, particularly regarding raw milk consumption.