Figure 1. The Premetastatic Niche Is Similar to an Inflammatory Nidus.

Both S100A8 and S100A9 induce the expression of SAA3 specifically in future metastasis sites in the lung, promoting Mac1+ myeloid and endothelial cell engraftment. In this process, SAA3 promotes its own secretion by a positive feedback mechanism mediated by TLR4 and induces NF-κB signaling pathway activation (left). This inflammation-like state accelerates the future recruitment of tumor cells (right).