Regulation of tumor metastasis by myeloid-derived suppressor cells.

Accumulation of pathologically activated immature myeloid cells with potent immune-suppressive activity is one of the major immunological hallmarks of cancer. In recent years, it became clear that in addition to their immune-suppressive activity, myeloid-derived suppressor cells (MDSCs) influence tumor progression in a variety of ways. They are directly implicated in the promotion of tumor metastases by participating in the formation of premetastatic niches, promoting angiogenesis and tumor cell invasion. In this review, we discuss recent data describing various roles of MDSCs in the formation of tumor metastases.