Immunological determinants of liver metastasis. Malignant cells and stromal cells that reside within the primary tumor release factors that engage liver-resident cells, including Kupffer cells, hepatocytes, and hepatic stellate cells. Inflammatory responses mounted by these cells induce myeloid cell accumulation and fibrosis, which form the basis of a pro-metastatic niche in the liver. ECM, extracellular matrix; IL-6, interleukin 6; SAA, serum amyloid A; TGF-β, transforming growth factor β; TIMP1, tissue inhibitor of metalloproteinases-1.