This study evaluated the effectiveness of extracellular vesicles (EVs) derived from RAW macrophage cell lines loaded with ۴T۱ breast cancer cell lysate as an immunotherapeutic strategy for breast cancer. A total of ۲۱ female BALB/c mice, aged ۶-۸ weeks and weighing ۱۵-۱۸ grams, were divided into three groups (n=۷). Tumor models were established in all mice through subcutaneous injection of ۴T۱ breast cancer cells, an aggressive and resistant cell line. RAW macrophages were cultured, stimulated with lipopolysaccharide (LPS), and loaded with ۴T۱ breast cancer cell lysates. The resulting EVs were administered over a ۳۵-day period. The mice were allocated into three groups: control, prophylaxis, and treatment. In the prophylaxis group, mice received three subcutaneous injections of macrophage-derived EVs loaded with ۴T۱ lysate at ۴-day intervals. Ten days after the final EV injection, they were injected with ۴T۱ cells to induce tumor formation. The treatment group received macrophage-derived EVs ۱۰ days after being injected with ۴T۱ cells, once palpable tumors had formed. The control group received no EV therapy. Survival rates were assessed throughout the study, showing no statistically significant differences between groups. On day ۷, ۷۱.۴% of mice in both the control and treatment groups were alive, while ۷۵.۸% of mice survived in the prophylaxis group (p=۰.۲). On day ۱۴, survival rates were ۱۰۰% in the control group, ۸۰% in the treatment group, and ۱۰۰% in the prophylaxis group (p=۰.۳). By day ۳۵, survival rates were ۵۰% in the control group, ۶۷.۷% in the treatment group, and ۱۰۰% in the prophylaxis group (p=۰.۱۳), with no significant differences in survival across the groups. However, significant reductions in tumor size were observed. On day ۷, the control group had an average tumor size of ۰.۳۲ ± ۰.۰۳ mm³, compared to ۰.۱۳ mm³ in the treatment group and no detectable tumors in the prophylaxis group (p=۰.۰۰۱). By day ۱۴, tumor sizes were ۵.۳۰۰ mm³ in the control group, ۲.۴۲۹ mm³ in the treatment group, and ۰.۰۱۷۱ mm³ in the prophylaxis group (p=۰.۰۰۱). On day ۳۵, tumor size reached ۲۴.۸۰۰ mm³ in the control group, ۲۲.۶۰۰ mm³ in the treatment group, and only ۰.۰۵۴۳ mm³ in the prophylaxis group (p=۰.۰۰۱). Repeated measurements over the course of the study confirmed that these tumor size differences were statistically significant (p=۰.۰۰۱). In conclusion, EVs derived from RAW macrophages and loaded with ۴T۱ breast cancer cell lysate significantly reduced tumor size in both the treatment and prophylaxis groups, particularly in the latter, where tumor growth was almost entirely inhibited. However, survival rates were not significantly improved. Further research is needed to explore the underlying mechanisms and potential clinical applications of this therapy.