Pathologists in Canada and France have identified what they believe are two of the most important tests for distinguishing between a benign growth on the mesothelial membrane and malignant mesothelioma.
Their work could be a key step toward better, more accurate mesothelioma diagnosis.
The Challenge of Mesothelioma Diagnosis
Associated almost exclusively with asbestos exposure, malignant mesothelioma is one of the most aggressive and lethal types of cancer. Fortunately, it is also extremely rare.
When a patient is believed to have mesothelioma, it is crucial for doctors to be able to quickly and accurately confirm the disease to optimize the patient’s odds of mesothelioma survival. But this is easier said than done.
Not only do many of the symptoms of mesothelioma mimic other less serious diseases, but non-cancerous growths on the mesothelial membranes around the lungs or abdomen can look just like mesothelioma in imaging studies.
To get around that problem and improve mesothelioma diagnosis, Canadian and French pathology researchers recently performed an extensive review of the medical literature on two fairly new types of molecular tests.
Gene Testing to Identify Mesothelioma
The first test is one to measure a suspected mesothelioma patient’s level of p16, a tumor suppressor protein encoded by a gene that is often deleted in people with mesothelioma.
Through an advanced type of test called fluorescence in situ hybridization (FISH), scientists can now detect p16 deletion which can be present in all types of mesothelioma, but is less frequent in peritoneal mesothelioma.
In their review of p16 FISH testing in suspected cases of mesothelioma, the researchers found that none of the people with beniqn mesothelial tumors tested positive for p16 deletion.
NOTE: A test that correctly rules out people without the condition (in this case, mesothelioma) is said to be highly “specific” for the condition.
A Second Type of Mesothelioma Test
The second test reviewed by the researchers was an immunohistochemical test for a molecular marker called BRCA1-associated protein (BAP1).
The loss of BAP1 is common in people with mesothelioma and several other types of cancers. Immunohistochemical testing for BAP1 loss involves examining suspected mesothelioma tissue for specific antigens.
As with the p16 FISH test, the researchers found that immunohistochemical testing for BAP1 loss was highly specific for mesothelioma; none of the people with benign disease exhibited BAP1 loss.
“In the context of a mesothelial proliferation, the finding of homozygous deletion of p16 by FISH or loss of BAP1 by immunohistochemistry is, thus far, 100% specific for malignant mesothelioma,” concludes Andrew Churg, MD, PhD, a pathologist at Vancouver General Hospital.
Although neither of the two tests are very sensitive for mesothelioma – meaning that they are not necessarily reliable ways to positively identify mesothelioma patients – their specificity makes them potentially valuable in the mesothelioma diagnostic process.
In addition, Dr. Churg suggests that the sensitivity of the two tests may be improved in cases of suspected mesothelioma by performing them together.
The findings appears in a recent issue of the Archives of Pathological and Laboratory Medicine.
Churg, A, et al, “New Markers for Separating Benign from Malignant Mesothelial Proliferations: Are We There Yet”?, April 2016, Archives of Pathological and Laboratory Medicine, pp. 318-321