['To demonstrate that exosomes (exo) could increase the therapeutic index of doxorubicin (DOX).', 'Exosomes were characterized by nanoparticle tracking analysis and western blot. Tissue toxicity was evaluated by histopathological analysis and drug efficacy by measuring tumor volume. DOX biodistribution was analyzed by MS.', 'Exosomal doxorubicin (exoDOX) avoids heart toxicity by partially limiting the crossing of DOX through the myocardial endothelial cells. For this reason, mice can be treated with higher concentration of exoDOX thus increasing the efficacy of DOX as demonstrated in breast and ovarian mouse tumors.'] Do exosomes increase the therapeutic index of doxorubicin in breast and ovarian cancer mouse models?