Serum amyloid A1 (SAA1) is a protein that in humans is encoded by the SAA1 gene. SAA1 is a major acute-phase protein mainly produced by hepatocytes in response to infection, tissue injury and malignancy. When released into blood circulation, SAA1 is present as an apolipoprotein associated with high-density lipoprotein (HDL). SAA1 is a major precursor of amyloid A (AA), the deposit of which leads to inflammatory amyloidosis. SAA1 has been a clinical indicator and reliable biomarker for inflammatory diseases, chronic metabolic disorders and late-stage malignancy. SAA1 has been extensively studied for its binding to HDL, with results suggesting a role in lipid metabolism. SAA1 has been associated with tumor pathogenesis, and its gene polymorphism is a contributing factor to certain types of malignant tumors. SAA1 has also been shown to affect the tumor microenvironment and contribute to tumor cell metastasis.