Decoding tumor microenvironment: EMT modulation in breast cancer metastasis and therapeutic resistance, and implications of novel immune checkpoint blockers.

Tumor microenvironment (TME) and epithelial-mesenchymal transition (EMT) play crucial roles in the initiation and progression of tumors. TME is composed of various cell types, such as immune cells, fibroblasts, and endothelial cells, as well as non-cellular components like extracellular matrix (ECM) proteins and soluble factors. These elements interact with tumor cells through a complex network of signaling pathways involving cytokines, growth factors, metabolites, and non-coding RNA-carrying exosomes. Hypoxic conditions within the TME further modulate these interactions, collectively influencing tumor growth, metastatic potential, and response to therapy. EMT represents a dynamic and reversible process where epithelial cells undergo phenotypic changes to adopt mesenchymal characteristics in several cancers, including breast cancers. This transformation enhances cell motility and imparts stem cell-like properties, which are closely associated with increased metastatic capability and resistance to conventional cancer treatments. Thus, understanding the crosstalk between the TME and EMT is essential for unraveling the underlying mechanisms of breast cancer metastasis and therapeutic resistance. This review uniquely examines the intricate interplay between the tumor TME and epithelial-mesenchymal transition EMT in driving breast cancer metastasis and treatment resistance. It explores the therapeutic potential of targeting the TME-EMT axis, specifically through CD73-TGF-β dual-blockade, to improve outcomes in triple-negative breast cancer. Additionally, it underscores new strategies to enhance immune checkpoint blockade (ICB) responses by modulating EMT, thereby offering innovative insights for more effective cancer treatment.