Tumor Markers

Tumor markers are substances produced by cancers or by other cells in response to cancer. The ideal tumor marker would be specific for a given type of cancer and would be absent in patients without cancer, would be sensitive enough to detect tumors early in disease, and would quantitatively reflect response to treatment. That said, most markers are made by normal cells as well as by cancer cells although they are usually produced at much higher concentrations in cancer. The markers can be proteins, enzymes, hormones, oncofetal antigens, receptors, metabolites, and genetic mutations. They can be detected in blood, urine, other fluids, and solid tissue. Some markers can even be associated with more than one tumor type. Unfortunately, not everyone with a particular tumor will have a higher level of tumor markers associated with that cancer. The major uses of tumor markers have included screening populations and high-risk groups; aiding in diagnosis of cancers (limited utility); staging of cancer; both predicting and monitoring response to therapy; and checking for recurrence of cancer. With rapidly evolving analytical technology more and more substances are being studied and identified as potential tumor markers. This chapter summarizes the use of some of the more established tumor markers.