A substance produced and released by tumor cells often exists in tumor cells or host body fluids in the form of metabolites such as antigens, enzymes and hormones. Tumors can be identified or diagnosed according to their biochemical or immune characteristics. What are tumor markers? The biochemical properties and metabolic abnormalities of tumor cells, so there are substances with qualitative or quantitative changes in the body fluids, excretions and tissues of tumor patients. These are tumor markers. http://www.modaivd.com/all-poct-products/tumor-markers/