Soluble mesothelin-related protein (SMRP), a protein found in the blood serum of some people, may not be as effective a biomarker for mesothelioma as it was once thought to be.
Malignant mesothelioma is a cancer of the internal membranes that surround the lungs, abdominal organs or heart. It is most often triggered by exposure to asbestos and is difficult to diagnose in its early stages. Biomarkers, like SMRP, are often used to try to make cancer diagnoses earlier since these compounds are often produced in larger quantities by cancer cells than by healthy cells.
But in a report in Clinical Chemistry and Laboratory Medicine, a team of researchers suggests that SMRP has some significant limitations when it comes to detecting mesothelioma. The biggest problem is that a number of factors other than mesothelioma, including lifestyle factors and kidney function, can also cause elevated SMRP levels. To address this issue and make SMRP more valuable for mesothelioma diagnosis, the team has developed an equation that takes into account some of these other SMRP-raising variables.
To design the equation, the team recruited 535 subjects who had been exposed to asbestos or silica (another lung lining irritant), many of whom were already suffering from asbestos-related disorders. They used linear regression models to quantify the strength of the relationship between SMRP and other clinical variables. According to their data, the strongest independent (non-cancer) influences on SMRP levels were age and glomerular filtration rate (GFR), a test used to check how well the kidneys are working. SMRP levels were also affected by smoking. SMRP demonstrated poor sensitivity (15.1%) for picking up non-malignant asbestos-related disorders, when compared to people who had been exposed to asbestos but were still healthy.
Although SMRP may not be the ideal biomarker for detecting early stage mesothelioma, it is still widely used as part of a battery of tests to diagnose the disease. To improve its diagnostic accuracy, the researchers based their new equation largely on age and GFR. However, they caution that, because of SMRP’s poor sensitivity, “Further work is needed to find new candidate biomarkers for diagnosing early stage mesothelioma.”