A tumor marker is a biomarker that can be used to indicate the presence of cancer or the behavior of cancers (measure progression or response to therapy). They can be found in bodily fluids or tissue. Markers can help with assessing prognosis, surveilling patients after surgical removal of tumors, and even predicting drug-response and monitor therapy. [1]
Tumor markers can be molecules that are produced in higher amounts by cancer cells than normal cells, but can also be produced by other cells from a reaction with the cancer. [2]
The markers can't be used to give patients a diagnosis but can be compared with the result of other tests like biopsy or imaging. [2]
Tumor markers can be proteins, carbohydrates, receptors and gene products. Proteins include hormones and enzymes. To detect enzyme tumor markers enzyme activity is measured. They were previously widely used, but they have largely been replaced by oncofetal antigens and monoclonal antibodies, due to disadvantages such as most of them lacking organ specificity. Carbohydrates consist of antigens on and/or secreted from tumor cells, these are either high-molecular weight mucins or blood group antigens. Receptors are used to determine prognosis and measure how the patient responds to treatment, while genes or gene products can be analyzed to identify mutations in the genome or altered gene expression.[ citation needed ]
Tumor markers may be used for the following purposes:
Tumor markers can be determined in serum or rarely in urine or other body fluids, often by immunoassay, but other techniques such as enzyme activity determination are sometimes used. Assaying tumor markers were significantly improved after the creation of ELISA and RIA techniques and the advancement of monoclonal antibodies in the 1960s and 1970s. [2]
For many assays, different assay techniques are available. It is important that the same assay is used, as the results from different assays are generally not comparable. For example, mutations of the p53 gene can be detected through immunohistochemical polymorphism screening of DNA, sequence analysis of DNA, or by single-strand conformational polymorphism screening of DNA. Each assay may give different results of the clinical value of the p53 mutations as a prognostic factor. [5]
Interlaboratory proficiency testing for tumor marker tests, and for clinical tests more generally, is routine in Europe and an emerging field [6] in the United States. New York state is prominent in advocating such research. [7]
The ideal tumor marker has the following characteristics:
An ideal tumor marker does not exist, and how they are clinically applied depends on the specific tumor marker. For example, tumor markers like Ki-67 can be used to choose form of treatment or in prognostics but are not useful to give a diagnosis, while other tumor markers have the opposite functionality. Therefore it's important to follow the guidelines of the specific tumor marker.
Tumor markers are mainly used in clinical medicine to support a diagnosis and monitor the state of malignancy or reocurrence of cancer. [4]