hCG Tumor Markers
Tumor markers are substances produced by the body, either by the tumor cells themselves or by the surrounding tissues as part of the body's immune system response to the tumor, according to the National Cancer Institute. These markers can be measured in either blood, urine or tissues samples, and are useful tools in cancer treatment. More than 12 different tumor markers have been identified, as different types of tumors will produce different substances. One such marker is human Chorionic Gonadotropin, or hCG.
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hCG
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hCG is a hormone normally produced during pregnancy, and is the marker measured by pregnancy tests. It is produced by specialized chorion cells which form a membrane that surrounds the developing fetus, and is detectable by laboratory tests within days of fertilization. According to MedicineNet.com, hCG's role is to stimulate development of the gonads, being either the testes or ovaries, hence the term gonadotropin. Some tumors also produce hCG.
Use in Cancer Care
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hCG markers have several different uses in cancer care. The presence of hCG can diagnose a tumor, as hCG is never present in healthy men and is present in healthy women only when they pregnant. During pregnancy, elevated levels of hCG can also be indicative of gestational cancer. During cancer treatment, hCG markers are used to determine whether a tumor is responding to therapy. A tumor that is shrinking should correspond to lowering levels of hCG, according to the National Cancer Institute. Followup care with patients in remission may also involve screening for hCG markers, to detect any recurring tumors.
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Cancers Detected With hCG
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Two different parts of the hCG molecules, called subunits, are used as tumor markers. The alpha subunit may be produced by tumors of the pancreas, pituitary or placenta. The beta subunit is secreted by tumors that originate in the ovaries and testicles. Beta subunit hCG is also a tumor marker for choriocarcinoma, a uterine tumor that originates from early embryonic cells and occurs during pregnancy. Choriocarcinoma is fast-growing and can spread to other organs, often the lungs, according to the National Cancer Institute.
Sensitivity
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The fertility market has driven industry to continually improve upon the sensitivity of hCG tests, such that laboratory tests of blood serum can now detect very minute levels of the hormone. This combined with the fact that even tiny tumors produce detectable amounts of hCG makes it a very effective tumor marker, according to TC-Cancer.com.
Considerations
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No tumor marker currently in use is perfect, and the possibility of false or misleading results always exists, according to Daniel Hoefner in the Medical Laboratory Observer. It is possible for a growing tumor to produce lowering hCG marker results owing to the fact that tumors are often made up of more than one type of cell, and not all of them will be secreting hCG. Also to consider is the fact that tests for hCG are most useful when performed serially: at diagnosis, and both during and following treatment. Should a laboratory change the type of test kit it uses for hCG detection during this time period, the levels of hCG shown could be skewed due only to the use of new or different chemicals.
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References
- National Cancer Institute: Tumor Markers: Questions and Answers
- MedicineNet.com: Definition of Human Chorionic Gonadotropin
- National Cancer Institute: Definition of Choriocarcinoma
- TC-Cancer.com: Tumor Markers; AFP, HCG, CA-125
- "Medical Laboratory Observer"; Serum tumor markers: Part II; Daniel M. Hoefner; February 2006
Resources
- Photo Credit Injection with Blood 3 image by Svenja98 from Fotolia.com
