The Tumor Microenvironment: Impact on Tumor Growth, Metastasis, and Therapeutic Resistance: A Systematic Review

Introduction: This systematic review assesses the role of the tumor microenvironment (TME) in cancer progression and therapy resistance by defining drug-microenvironment interactions and determining the molecular determinants in the TME that could help improve the efficacy of administered treatments and alleviate existing adverse effects. Methods: This systematic review follows the PRISMA protocol and the PICOS selection framework to retrieve studies from PubMed/MEDLINE, Web of Science, Scopus, and the Cochrane Library. Only original human-related research published in English between 2008 and 2023 was used to explore the reciprocal relation between tumor cells and TME components. The ROBINS-I tool assessed the risk of bias. Results: Out of 258 articles initially identified, 15 met the inclusion criteria for this review. The results showed that TMEs significantly influence treatment outcomes in cancer progression, metastasis, and drug resistance. Focusing on TMEs like CAFs, immune cells, and ECM enhances drug efficacy. The study highlighted potential strategies to improve drug delivery, suppress metastatic processes, and restore immune function, ultimately leading to better outcomes for cancer patients. Discussion: Original evidence suggests that Cancer-Associated Fibroblasts (CAFs), immune cells, and Extracellular Matrix (ECM) contribute to therapeutic resistance and metastasis within the TME. They also promote metastasis by inducing Epithelial- Mesenchymal Transition (EMT) and affecting Cancer Stem Cell (CSC) populations. Moreover, the immunosuppressive TME consists of regulatory T cells and myeloidderived suppressor cells that allow tumors to evade the immune system, a concern for immunotherapy. Conclusion: The TME plays a vital role in cancer development, metastasis formation, and therapy failure. The perspectives for innovative ECM-modulating treatments and interventions targeting the direct interactions between TME and cancer cells can be revolutionary and suggest better outcomes for treatment-naïve and refractory cancers. Future research should use these results as inputs to apply clinical and therapy studies to enhance cancer management outcomes.