Therapeutic potentials of mesenchymal stem cell-derived exosomes for major solid malignancies: A narrative systematic review

Treatments for solid tumors, the most common malignant neoplasms, are often confounded by tumor microenvironments that impede the achievement of uniform anti-tumor effects throughout the entire malignant mass, which contributes to recurrence and progression, negatively impacting clinical outcomes. Improved treatment methods for solid malignancies are therefore needed. Mesenchymal stromal cells (MSCs) have been investigated for treatments for various types of solid tumor cancers due to their ability to target tumor cells with similar cell surface protein profiles. MSC-derived exosomes (MSC-Exos) elicit many of the tumor cell responses produced by MSC with no potential for differentiation and reduced risks of adverse effects. We surveyed the literature and clinical trials registries to identify studies investigating MSC-Exo-based anti-cancer therapies for gastric cancer, colorectal cancer, breast cancer, lung cancer, brain cancer, pancreatic cancer, and urological malignancies, and summarize the results of relevant studies herein to provide a comprehensive description of the therapeutic effects and potential clinical applications of MSC-Exos for the treatment of solid tumor malignancies. We include a summary of relevant clinical trials performed to date in an attempt to assess the data available regarding MSC-Exo safety, and propose future efforts regarding the requirements for transitioning forward from phase-1, 2 trials.