Myeloid-derived suppressor cells (MDSCs) are pathologically arisen cells mainly acknowledged for their role in immune suppression. Studies have investigated different phenotypes of MDSCs and related indices, for example, numbers, frequency, and percentage. Mostly, they point out the increased levels of MDSCs in patients with different cancers and their close correspondence with metastasis to the lymph nodes and distant organs. Different mechanisms have been proposed to contribute to cancer metastasis by MDSCs, mainly including tumor cells’ circulation and proliferation, angiogenesis, matrix remodeling, lipid transfer, and neutrophil extracellular traps’ formation. MDSCs have been a great facilitator of tumor initiation, invasion, and metastasis to different organs, mainly involving the lymph nodes, brain, peritoneum, lung, and liver. Chemokines and their ligands are the main molecules involved in the chemoattraction of MDSCs to the premetastatic niches, causing inflammatory sites that express high levels of chemokines a convenient home for MDSCs’ recruitment and metastases. Targeting signaling pathways of these chemokines might offer to prevent/treat cancer metastasis by inhibiting the MDSCs’ recruitment. This chapter reviews MDSCs’ subsets and phenotypes associated with metastasis in the context of breast, lung, gastrointestinal, and other types of cancer.