Plasticity of myeloid-derived suppressor cells in cancer

•Myeloid-derived suppressor cells (MDSC) are critically important for regulation of immune responses in cancer.•MDSC have distinct features separating them from neutrophils and monocytes.•Monocytic MDSC differentiate in tumor sites to macrophages and dendritic cells.•This process is shaped by tumor microenvironment.•In recent years, specific mechanisms regulating M-MDSC differentiation start to emerge.