At the later stage, tumor cells escaping the killing effect of KCs can further utilize various growth factors such as interleukin- 6 (IL-6), hepatocyte growth factor (HGF), VEGF, and MMP-9 secreted by M2-type KCs to form an environment suitable for tumor cells to proliferate; thus liver metastasis is formed (62). Here, MMP9 is linked to neoplasm.