Mesothelioma blood tests are not sufficient to diagnose the disease on their own.
Researchers are working to improve these blood tests as a standalone diagnostic tool.
Mesomark, Osteopontin, N-ERC/Mesothelin and Fibulin-3 are the four assays available.
Imaging tests can be helpful in diagnosing of mesothelioma, but definitive diagnosis usually requires a procedure to obtain a biopsy. Ideally, however, physicians would be able to order a set of blood tests that could identify the presence of mesothelioma without a biopsy. These tests would detect abnormal substances, called biomarkers, given off by the cancer and circulating in the bloodstream.
Biomarker tests – also called assays – have been used successfully in diagnosing and monitoring certain types of cancer including breast cancer and colon cancer. However, mesothelioma biomarkers that have been developed for clinical use are not sensitive enough to diagnose mesothelioma without additional testing. Nevertheless, there may be a role for these biomarkers in determining prognosis and for tracking progression of the disease. Immunohistochemical marker panels are also a form of blood test that have shown success in differentiating between malignant pleural mesothelioma and lung adenocarcinoma to help prevent misdiagnosis. Moreover, additional research may shed light on new biomarkers that could someday diagnose mesothelioma using a simple blood test.
Mesothelin is a glycoprotein (i.e., a sugar molecule combined with a protein molecule) that is produced by normal mesothelium, but is produced in tremendous amounts by malignant mesothelioma. When malignant mesothelioma produces so much mesothelin, it also produces related molecules that can dissolve in the blood.
The Mesomark assay is a commercial blood test that detects soluble mesothelin-related peptides (SMRPs). The theory behind Mesomark is that if SMRPs are detected in a person’s blood, that person likely has malignant mesothelioma. While the Mesomark assay has been approved by the FDA for use in the diagnosis and management of mesothelioma, the sensitivity of the assay is low, ranging from 19% to 68%. This low sensitivity is the main reason the Mesomark assay is not considered sufficient to diagnose mesothelioma by itself, but still helpful for mesothelioma screening.
Osteopontin is a glycoprotein whose levels increase substantially when the body develops various types of cancer, including mesothelioma. In one clinical study, osteopontin levels were approximately twice as high in the blood of individuals with pleural mesothelioma as those without the cancer. However, since osteopontin levels can also increase due to a number of other conditions such as ischemic stroke, kidney stones, and other cancers, it is cannot be used as a definitive blood test for mesothelioma.
N-ERC/Mesothelin is a protein fragment of mesothelin secreted into the bloodstream. By using the very sensitive measure of this soluble protein, researchers have been able to use N-ERC/mesothelin levels in the blood to detect the presence of mesothelioma. Initial results from this test have been quite promising, with researchers reporting that the sensitivity of the N-ERC/mesothelin test was 95% and sensitivity was 76% in plasma. If these results are confirmed through additional testing, the N-ERC/mesothelin would be one of the most accurate single tests available for diagnosing mesothelioma.
Fibulin-3 is a glycoprotein that is present in higher concentrations in people with pleural mesothelioma compared to those without the cancer. Initial results of clinical studies examining the use of fibulin-3 were extremely promising. Researchers reported sensitivity and specificity levels of 97% and 96% respectively, which is an acceptable sensitivity rate for diagnostic testing.
However, more recently studies have found that the accuracy of the fibulin-3 test may not be as high as previously reported. Nonetheless, testing for the glycoprotein may still be useful to determine a patient’s prognosis. Fibulin-3 levels in the blood may also help physicians track the progression of malignant mesothelioma and follow a patient’s treatment progress. In addition, fibulin-3 may be extremely accurate in distinguishing between mesothelioma and benign lung and pleural diseases.