A New Test for Mesothelioma?

Malignant pleural mesothelioma, an aggressive cancer of the pleural membrane that encases the lungs, can be difficult to diagnose.  Early symptoms of the disease can be vague and mimic other lung conditions.  But the longer a patient goes without a firm diagnosis, the poorer the prognosis is likely to be since mesothelioma is resistant to many traditional therapies.

In addition to considering the patient’s symptoms and history of asbestos exposure, doctors often rely on biomarkers – compounds found in the blood or lung fluid – to pinpoint mesothelioma. Now, a group of Danish scientists are investigating a new biomarker that may eventually allow for an earlier, more accurate, mesothelioma diagnosis.

Methylthioadenosine phosphorylase (MTAP) is a key enzyme used to help cells recycle adenosine triphosphate (ATP). But MTAP is often missing in mesothelioma cells.  The goal of the Danish researchers was to determine whether the loss of MTAP could be detected with immunohistochemistry testing and used as a diagnostic marker.

To test the possibility, the team measured the levels of MTAP in the lung fluid of 99 mesothelioma patients as well as 39 patients who had a different condition called reactive mesothelial proliferations (RP).  They found that 64 out of 99 (65%) mesothelioma patients had decreased MTAP expression, while only 23% of the RP patients showed the same decrease. They took their testing a step further by using a different double-staining testing method on the coagulated pleural fluid of another 14 mesothelioma patients and 20 RP patients.  In these samples, they found that decreased MTAP expression could diagnose mesothelioma with 71% sensitivity and 90% specificity.

In a report of their findings in the medical journal Histopathology, the team concludes “Decreased MTAP expression could potentially be useful in combination with other markers in the diagnosis of malignant pleural mesothelioma.”

Some of the other mesothelioma biomarkers already in use include mesothelin-related peptide (SMRP, the MesoMark test), osteopontin, and soluble mesothelin.

Sources:

Zimling, ZG, “The diagnostic value of immunohistochemically detected methylthioadenosine phosphorylase deficiency in malignant pleural mesothelioma”, March 6, 2012, Histopathology, Epub ahead of print.
Creaney, Jenette, “Serum and pleural fluid biomarkers for mesothelioma”, July 2009, Current Opinion in Pulmonary Medicine, pp. 366-370.
“Discovery and Validation of Potential Genomic-Based Biomarkers for Asbestos Related Neoplasms”, American Australian Mesothelioma Consortium and NYU Mesothelioma Biomarker Discovery Laboratory.