Similar to TAMs, it is likely that MDSCs are stimulated by a variety of soluble factors, such as GM-CSF, VEGF, TNF-α, PGE2, IL-1β, IL-6, and IL-10, which are secreted by tumor and infiltrating immune cells, as well as tumor-associated fibroblasts (148) (Figure 2C). Here, CSF2 is linked to neoplasm.