Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid cells that accumulate in the tumor microenvironment and contribute to immune evasion and tumor progression. Initially identified as granulocytes or monocytes, MDSCs were later characterized as a distinct population of multipotent progenitor cells. Their discovery has significantly advanced our understanding of tumor biology, neoplastic progression, and immune adjuvant therapy. MDSCs influence tumor progression and metastasis through their ability to suppress T-cell function, inhibit immune responses, and promote tumor angiogenesis. They interact with tumor cells and the host macroenvironment, and their expansion is influenced by tumor-secreted cytokines and chemokines. MDSCs can be classified into subsets, such as granulocytic-MDSCs (G-MDSCs) and monocytic-MDSCs (Mo-MDSCs), based on their morphology and surface markers. G-MDSCs are the predominant subset in tumor-bearing mice. MDSCs are regulated by various factors, including growth factors, cytokines, and the tumor microenvironment. They play a critical role in tumor progression by promoting angiogenesis, tumor invasion, and metastasis. MDSCs also regulate host defense by suppressing immune responses and facilitating tumor immune evasion. Targeting MDSCs is a promising therapeutic strategy for cancer treatment, as their inhibition can reduce tumor growth, metastasis, and improve survival. Current research focuses on understanding the mechanisms underlying MDSC function and developing targeted therapies to modulate their activity.Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid cells that accumulate in the tumor microenvironment and contribute to immune evasion and tumor progression. Initially identified as granulocytes or monocytes, MDSCs were later characterized as a distinct population of multipotent progenitor cells. Their discovery has significantly advanced our understanding of tumor biology, neoplastic progression, and immune adjuvant therapy. MDSCs influence tumor progression and metastasis through their ability to suppress T-cell function, inhibit immune responses, and promote tumor angiogenesis. They interact with tumor cells and the host macroenvironment, and their expansion is influenced by tumor-secreted cytokines and chemokines. MDSCs can be classified into subsets, such as granulocytic-MDSCs (G-MDSCs) and monocytic-MDSCs (Mo-MDSCs), based on their morphology and surface markers. G-MDSCs are the predominant subset in tumor-bearing mice. MDSCs are regulated by various factors, including growth factors, cytokines, and the tumor microenvironment. They play a critical role in tumor progression by promoting angiogenesis, tumor invasion, and metastasis. MDSCs also regulate host defense by suppressing immune responses and facilitating tumor immune evasion. Targeting MDSCs is a promising therapeutic strategy for cancer treatment, as their inhibition can reduce tumor growth, metastasis, and improve survival. Current research focuses on understanding the mechanisms underlying MDSC function and developing targeted therapies to modulate their activity.