IL6 and neoplasm: In the pdgfbret/ret mouse model, PCs deficiency-driven hypoxia result in IL-6 upregulation and an increased myeloid-derived suppressor cell (MDSC) transmigration in tumors, and the MDSC accumulation leads to increased tumor growth, while the amounts of circulating malignant cells can be abrogated upon the recovery of PC coverage (Figure 1, process ➂) (Hong et al., 2015).