Background Cancer is a major cause of death worldwide and most of the therapeutic approaches are relatively ineffective in eliminating cancer especially due to drug resistance. As an alternative, therapy with live microorganisms can induce a robust proinflammatory and anti-cancer immune response in the microenvironment of the tumor. In the present study, we aimed to establish a model for taking the advantages of immune responses against intracellular protozoan parasites for cancer treatment. Methods Leishmania infantumandL. tropicawere used in our study as agents of visceral and cutaneous forms of the infection, respectively. After establishing 4T1 breast cancer in mice groups, live-attenuatedL. infantum(At-Li) and live-attenuatedL. tropica(At-Lt) treatments were performed and results were evaluated according to tumor volume, immune markers and histological examination. Results Live-attenuatedLeishmaniastrains regressed 4T1-breast cancer in mice and are nonpathogenic, and these strains induce an immune response against 4T1 breast cancer. It is shown that At-Lt is found to be more effective than At-Li in breast cancer treatment using different methods included in the study as analyses of immune parameters, and histopathological examination in tumor tissue besides spleen cells. The tumor grew more slowly by the immune-stimulant effect of live-attenuatedLeishmaniaparasites. Conclusion This promising therapy should be investigated for optimization in further studies with different cancer types andL. tropicamay be designed to express antigens to enhance tumor antigen-specific responses, which may further improve efficacy and immune memory development.