A tumor marker is a substance found in the blood, urine, or body tissues that can be elevated in cancer, among other tissue types. 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.
Tumor markers can be produced directly by the tumor or by non-tumor cells as a response to the presence of a tumor. Most tumor markers are tumor antigens, but not all tumor antigens can be used as tumor markers.
Together with Mammography, Ultrasonography, CT Scan and MRI, the Tumor Marker is not a diagnostic test. The diagnostic test should be done by biopsy.
Diagnosis of specific tumor types, particularly in certain brain tumors and other instances where biopsy is not feasible.
As stated in the BMJ 2009, tumour 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, screening purposes. The use of these tests without understanding their utility has resulted in inappropriate use of tumour marker blood tests, which has also resulted in further inappropriate over-investigation for cancers.
If repeated measurements of tumor marker are needed, some clinical testing laboratories provide a special reporting mechanism, a serial monitor, that links test results and other data pertaining to the person being tested. This requires a unique identifier for the person. In the United States commonly a Social Security number & Civil Personal Record (CPR) in Bahrain are used for this. One important function of this mechanism is to ensure that each test is performed using the same assay kit. For example, for AFP many different commercial assay kits, based on different technologies, are available. AFP measurements obtained using different assay kits are not comparable unless special calculations are performed.
Interlaboratory proficiency testing for tumor marker tests, and for clinical tests more generally, is an emerging field.In the United States, New York state is prominent in advocating such research.
The high dose hook effect is an artefact of tumor marker immunoassay kits, that causes the reported quantity of tumor marker to be incorrectly low when the quantity is high. An undetected hook effect may cause delayed recognition of a tumor. The hook effect can be detected by analyzing serial dilutions. The hook effect is absent if the reported quantities of tumor marker in a serial dilution are proportional to the dilution.
Multiple Tumor marker test
There are 4 things of Tumor marker test should be considered:
Sensitivity, no Tumor marker test has 100 percent sensitivity, so some tumor sre still not detected by a single Tumor marker test
Specificity, only M2-PK Tumor marker test for colocteral has up to 95 percent specificity
False Negative, the result is negative, but in fact is positive, so it is very dangerous; until now only M2-PK Tumor marker test which analyze the DNA has no false negative
False Positive, the result is positive, but in fact is negative, because the test result is positive, so another test(s) or biopsy should be done
Multiple Tumor marker test will give more exact result, it are:
Colorectal: M2-PK, if M2-PK is not available, so can test CEA, CA 19-9, CA 125
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