en Blood and Immune System Blood and Immune System Experimental research article Experimental research article <div style="text-align: justify;"><strong><span class="fontstyle0">Introduction: </span></strong><span class="fontstyle2">Breast cancer is one of the important causes of mortality among women. Many studies have focused on the development of natural health products for prevention and treatment of breast cancer. This study investigated the effects of </span><span class="fontstyle3">Bifidobacterium bifidum </span><span class="fontstyle2">and its microvesicles (MVs) on 4T1-induced breast cancer in BALB/c mice. </span><span class="fontstyle0"><strong>Methods:</strong> </span><span class="fontstyle2">Sixty female BALB/c mice were divided into 5 groups: (1) negative control, (2) positive control, (3) doxorubicin, (4) probiotic and (5) MVs (isolated from </span><span class="fontstyle3">B. bifidum</span><span class="fontstyle2">). The mice in groups 4 and 5 were pretreated with </span><span class="fontstyle3">B. bifidum </span><span class="fontstyle2">and MVs for 4 weeks, respectively. Tumor was induced by subcutaneous administration of 4T1 cell culture. After tumor development, mice in group 3 were treated with doxorubicin while other groups were treated as before. The mice were sacrificed after 3 weeks, breast tumors were removed and histologically examined. Also, P53 and Ki67 protein were evaluated by immunohistochemistry staining, and P53 gene expression was assessed by RT-PCR. </span><span class="fontstyle0"><strong>Results:</strong> </span><span class="fontstyle2">Pretreatment with MVs and probiotic reduced mortality and tumor growth rate. MVs and Probiotic prevented the weight loss and suppressed tumor cell proliferation which was indicated by Ki-67 and p53. The expression of p53 confirmed these results. Despite the malignancy in the breast tissue, necrosis of cancer cells occurred in the mice treated with MVs. </span><strong><span class="fontstyle0">Conclusion: </span></strong><span class="fontstyle2">MVs of </span><span class="fontstyle3">B. bifidum </span><span class="fontstyle2">effectively inhibited breast cancer development in mice and suppressed tumor cell proliferation. Probiotic microorganisms and their metabolites can be used as a functional food to prevent breast cancer.</span></div> Triple negative breast cancer, Probiotic, Bifidobacterium bifidum, Microvesicles, Ki67, p53 333 344 http://ppj.phypha.ir/browse.php?a_code=A-10-1421-1&slc_lang=en&sid=1 Farzanrh Nazari 3200319475328460031326 3200319475328460031326 No Microbiology Department, Science Faculty, Islamic Azad University , Arak Branch, Arak, Iran Parvaneh Jafari p-jafari@iau-arak.ac.ir 3200319475328460031327 3200319475328460031327 Yes Microbiology Department, Science Faculty, Islamic Azad University , Arak Branch, Arak, Iran Bizhan Nomanpour 3200319475328460031328 3200319475328460031328 No School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran Kamibiz Varmira 3200319475328460031329 3200319475328460031329 No Research Center of Oils and Fats, Kermanshah University of Medical sciences, Kermanshah, Iran Farshid Reissi 3200319475328460031330 3200319475328460031330 No School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran