Abstract: Macrophagses are important components of the liver microenvironment, and play an essential role in the occurrence and development of liver metastasis of digestive system malignancies. Macrophages and liver sinusoidal endothelial cells constitute the first defense line of the liver, which can rapidly recognize and arrest the circulating tumor cells invading into the liver sinusoidal, by phagocytosis or promoting their apoptosis, thus play a cytotoxic effect to inhibit the occurrence of liver metastases. On the other hand, macrophages can combine to the circulating tumor cells and be activated. As a result, hepatocyte growth factor and other cytokines were released, which significantly promoted the proliferation of tumors cells, and thus promoting liver metastases. It may provide a new idea in preventing and treating liver metastasis of digestive system malignancies by targeting macrophages during tumor immunotherapy

Key words: Macrophages, Neoplasm metastasis, Tumor microenvironment