The results of this study provide the first insights into the role of lactadherin in metastatic BC cell-secreted sEVs as inductors of metastatic capacity in less aggressive recipient cells in vitro and in vivo in a peritoneal carcinomatosis mouse model, supporting the possibility of using lactadherin in sEVs as a new therapeutic agent for this disease. Here, MFGE8 is linked to breast cancer.