Tumor marker

A tumor marker is a biomarker found in blood, urine, or body tissues that can be elevated by the presence of one or more types of cancer. There are many different tumor markers, each indicative of a particular disease process, and they are used in oncology to help detect the presence of cancer. An elevated level of a tumor marker can indicate cancer; however, there can also be other causes of the elevation (false positive values).

Tumor markers can be produced directly by the tumor or by non-tumor cells as a response to the presence of a tumor.

Although mammography, ultrasonography, computed tomography, magnetic resonance imaging scans, and tumor marker assays help in the staging and treatment of the cancer, they are usually not definitive diagnostic tests. The diagnosis is mostly confirmed by biopsy.

On the basis of their chemical nature tumor markers can be proteins, conjugated proteins, peptides or carbohydrates. Proteins or conjugated proteins may be enzymes, hormones or fragments of proteins. Sequencing of genes for diagnostic purposes is mostly classified under the biomarker heading and is not treated here.

Tumor markers may be used for the following purposes:

As stated in the BMJ 2009, tumor markers should not generally be used for the purpose of diagnosis of cancers, as opposed to monitoring purposes in certain cancers, or in certain cases, for screening purposes. The use of these tests without understanding their utility has resulted in inappropriate use of tumor marker blood tests, which has resulted in inappropriate over-investigation for cancers.

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. Microscopic visualization in tissue by does not give quantitative results and is not considered here.

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