 The SMRP levels correlate directly with tumor volume thus permitting less invasive monitoring and improved assessment of treatment response.The MESOMARK assay is the most well-known and the world's first blood serum-based test for diagnosing mesothelioma.However, as certain types of tumors (such as sarcomatoid mesothelioma) do not release SMRP, the FDA recommends that doctors use the MESOMARK assay in conjunction with other tests to ensure an accurate mesothelioma diagnosis.