Pathologists in France and Canada have been able to identify what they believe are two of the most important tests to distinguish between benign growth on the membrane around the lungs and the asbestos-related cancer mesothelioma.
This research could be a step toward improved and more accurate mesothelioma diagnosis.
What is mesothelioma?
Mesothelioma is an incurable cancer caused, in the vast majority of cases, by exposure to asbestos dust and fibres.
Figures from the Health and Safety Executive show that more than 2,500 people are diagnosed with mesothelioma in the UK each year and according to the Department for Health and Pensions, 53,000 people will die from mesothelioma between 2013 and 2037.
Mesothelioma is found in the lining of the lungs, known as the pleural membrane (or pleura). This membrane is meant to protect the lungs and aid its smooth movement while breathing.
It is typically fatal within one year of diagnosis, but research into potential treatments is improving.
Difficulty diagnosing mesothelioma
Mesothelioma can be difficult to diagnose. Many of the usual tests specialists use to diagnose lung diseases prove unreliable when they are used to try and diagnose mesothelioma. In some cases, people have to undergo surgery to find out what is wrong or it is not diagnosed until after death through a post-mortem examination.
When a patient is believed to have mesothelioma, it is crucial for doctors to be able to quickly and accurately confirm the disease to optimise the patient’s odds of a prolonged survival.
Not only do many of the symptoms of mesothelioma mimic and appear to be like other less serious lung diseases, tumorous mesothelioma growths around the lungs can look just like non-cancerous growths in imaging studies.
To try and get around difficulties and improve mesothelioma diagnosis, Canadian and French pathology researchers have recently performed an extensive review of medical literature on two fairly new types of molecular tests.
Identifying mesothelioma with gene testing
The first test is used to measure patients’ level of p16, a protein that suppresses tumours, encoded by a gene that is often ‘deleted’ or ‘destroyed’ in people with mesothelioma.
Through an advanced type of test called “fluorescence in situ hybridisation” (FISH), scientists can now detect p16 deletion which can be present in all types of mesothelioma.
In the review of p16 FISH testing in suspected cases of mesothelioma, researchers found that none of the people with benign, non-cancerous tumours tested positive for p16 deletion.
Identifying mesothelioma with immunohistochemistry tests
The second test reviewed by the researchers was an immunohistochemistry test for a molecular marker called BRCA1-associated protein (BAP1).
Immunohistochemistry (IHC) refers to the process of detecting antigens (e.g. proteins) in cells of a tissue by exploiting the principle of antibodies binding specifically to antigens in tissue. Immunohistochemical staining is widely used in the diagnosis of abnormal cells such as those found in cancerous tumours.
The loss of BAP1 is common in people with mesothelioma and several other types of cancers. Immunohistochemistry testing for BAP1 loss involves examining suspected mesothelioma tissue for specific antigens.
As with the p16 FISH test, researchers found that immunohistochemistry testing for BAP1 loss was highly specific for mesothelioma; none of the people with benign, non-cancerous tumours showed BAP1 loss.
Specificity and sensitivity
A test that correctly rules people out of having a condition (in this case mesothelioma) is said to be highly “specific” for testing the desired condition.
Although neither of the two tests are very “sensitive” for mesothelioma – meaning that they are not necessarily a reliable way to positively diagnose mesothelioma in patients – their “specificity” makes them potentially valuable in future mesothelioma diagnostic processes.
Dr Andrew Churg, a pathologist at Vancouver General Hospital, suggests that the sensitivity of the two tests may be improved in cases of suspected mesothelioma by performing them together.