The article provides a comprehensive overview of myeloid-derived suppressor cells (MDSCs) and their role in tumor progression and metastasis. Initially identified as granulocytes or monocytes, MDSCs are now recognized as a population of multi-potent progenitor cells that exhibit immunosuppressive activities. The discovery and study of MDSCs have significantly advanced our understanding of tumor pathobiology and neoplastic progression, influencing approaches to immune adjuvant therapy. The authors discuss the historical context of MDSCs, their influence on tumor progression and metastasis, and the crosstalk between tumor cells, MDSCs, and the host macroenvironment. They highlight the bidirectional molecular crosstalk between tumor cells and myeloid progenitor cells, leading to immune evasion and tumor vascularization. The article also reviews the phenotypic heterogeneity of MDSCs, their regulation by tumor-secreted factors, and their impact on host defense and therapeutic responses. Finally, the authors emphasize the potential of MDSCs as therapeutic targets and regulators of cancer therapy, noting the need for further research to elucidate the mechanisms underlying their abnormal differentiation and function.The article provides a comprehensive overview of myeloid-derived suppressor cells (MDSCs) and their role in tumor progression and metastasis. Initially identified as granulocytes or monocytes, MDSCs are now recognized as a population of multi-potent progenitor cells that exhibit immunosuppressive activities. The discovery and study of MDSCs have significantly advanced our understanding of tumor pathobiology and neoplastic progression, influencing approaches to immune adjuvant therapy. The authors discuss the historical context of MDSCs, their influence on tumor progression and metastasis, and the crosstalk between tumor cells, MDSCs, and the host macroenvironment. They highlight the bidirectional molecular crosstalk between tumor cells and myeloid progenitor cells, leading to immune evasion and tumor vascularization. The article also reviews the phenotypic heterogeneity of MDSCs, their regulation by tumor-secreted factors, and their impact on host defense and therapeutic responses. Finally, the authors emphasize the potential of MDSCs as therapeutic targets and regulators of cancer therapy, noting the need for further research to elucidate the mechanisms underlying their abnormal differentiation and function.