Biomarkers and Blood Tests for Mesothelioma
Testing for mesothelioma is never straightforward. Most patients will have to undergo multiple diagnostic tests to either have a confirmed diagnosis or to rule this out as a possibility. Most diagnostic journeys for mesothelioma begin with a physical exam, continue on to imaging screenings, and include biopsies of suspected tissues or fluids. Blood tests, used to look for biomarkers indicative of cancer generally, and mesothelioma specifically, may also be part of the process.
Biomarkers in the Blood
A biomarker is a molecule, of biological origin, that is found in tissues, blood, or other bodily fluids and is characteristic of some process or disease. A biomarker is not necessarily a bad thing. For instance certain hormones in urine are biomarkers that can indicate that a woman is pregnant. These biomarkers have been useful in also diagnosing diseases and conditions, including cancer.
Various types of biomarkers can be found in the blood to indicate the presence of cancer in the body. These include certain proteins, nucleic acids like DNA and RNA, antibodies, those substances used by the immune system uses to recognize foreign substances, and others. If there is a biomarker that cancer cells are known to produce, its presence in the blood can be part of an overall diagnosis. Some biomarkers are general to all types of cancers, while others may indicate a specific type.
SMRPs and the MESOMARK Assay
One of the most specific biomarkers for mesothelioma is called SMRP. It stands for soluble mesothelin-related proteins. These proteins are produced and released by cancer cells of the mesothelium. They are normal in mesothelium cells, but often overproduced in cancerous cells. The MESOMARK assay is a blood test that measures levels of SMRP.
Studies have shown that the MESOMARK assay can be a useful diagnostic tool because most patients with mesothelioma have elevated levels of SMRPs compared to healthy people. Unfortunately this is not a fool-proof test. Some patients with mesothelioma do not have elevated levels. In addition to diagnosing the cancer, MESOMARK can also be used to track the progress of the condition. In patients with mesothelioma, levels of SMRP usually go up as the condition gets worse.
There is a great potential for SMRP as a biomarker to act as an early test for mesothelioma. People who have been exposed to asbestos could be screened using the assay to detect rising levels of SMRP early and to get an earlier diagnosis and better treatment.
Another test used to detect mesothelin proteins is the N-ERC/mesothelin test. It is similar to the MESOMARK assay, but is possibly more accurate, thanks to the use of a special enzyme to detect the proteins. While this newer test is more accurate, it is still not a definitive biomarker test for the same reasons that the MESOMARK test is not.
Another biomarker for mesothelioma is the protein fibulin-3. Like SMRP it is released in quantities that are greater than normal in mesothelioma cancer cells. The protein can be found in blood and in pleural fluid. One early study using fibulin-3 as a biomarker found that it was 95 percent at ruling out mesothelioma and more than 96 percent more effective at detecting it. Not all studies have found such promising results, so research into this biomarker as a diagnostic test are ongoing.
Osteopontin is another protein that is typically found at higher levels in the blood of patients with mesothelioma, compared to healthy people. There are, however, other types of cancer that also elevate the levels of this bone-related protein in the blood. These include lung cancer, breast cancer, and colon cancer.
Where tests for osteopontin may be most useful is in screening people who were known to have been exposed to asbestos. There is a strong connection between the levels of this biomarker and the extent to which a person was exposed to asbestos. It may be useful in figuring out just how much exposure a person received, and therefore, the level of risk of later developing mesothelioma.
Another potentially useful biomarker is megakaryocyte potentiation factor, or MPF. This is a protein made by a precursor of mesothelin. No one has yet figured out what MPF does in the body, but it has been detected at very high levels in people known to have mesothelioma. Other types of cancer may cause elevated levels of MPF, like ovarian and pancreatic cancer.
One study found that levels of MPF changed before and after surgery to remove mesothelioma tumors. The amount of MPF in the blood varied depending on how much of the tumor could be removed. This means it could be a useful test for determining how much cancerous tissue remains after a surgery and how successful a surgery has been.
Tracking Biomarkers in at-Risk Patients
Blood tests for biomarkers have great potential to detect mesothelioma in patients, but there are limitations. Research will continue as scientists look for better tests that can more accurately and specifically diagnose this terrible type of cancer. In the meantime, these biomarker blood tests have another important role to play: monitoring risk in people exposed to asbestos.
Where blood tests could be more useful for patients at risk for mesothelioma is in tracking the presence of biomarkers that indicate cancer. If you have been exposed to asbestos, for example, your doctor could test you regularly for multiple biomarkers, some specific to mesothelioma, others generally for cancer. These tests could help your doctor determine earlier if you are developing cancer.
From that early determination you could then be tested more rigorously for cancer and potentially get a much earlier diagnosis than would have been possible otherwise. With an earlier diagnosis, you would have the ability to choose a better treatment plan, attack the cancer aggressively, and have a better chance of living longer or even beating the cancer entirely. More research is needed to develop more and better blood tests for mesothelioma biomarkers, but the potential is there and the promise is great that these tests can help more people and save lives.
- http://www.nejm.org/doi/full/10.1056/NEJMoa1115050 - t=article
- http://www.nejm.org/doi/full/10.1056/NEJMoa051185 - t=article
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