Figure 1. Mechanisms of MIF-dependent tumor growth and metastasis. Factors produced by incipient tumors induce monocytic and granulocytic myeloid-derived suppressor cells (MDSCs) in the circulation, spleen and within the tumor. The production of macrophage migration inhibitory factor (MIF) by tumor cells leads to an increased abundance of monocytic MDSCs within the tumor, through enhanced recruitment, expansion or local differentiation. Monocytic MDSCs suppress antitumor immune responses, de facto underlying the MIF-induced stimulation of tumor growth and metastasis. MIF inhibition maybe a valuable approach for the prevention of metastatic disease by targeting the host microenvironment.