Diagnosing Mesothelioma with BAP1 Testing: Does it Work?

Tests for the presence or absence of the BAP1 tumor-suppressor protein are likely to continue to play a pivotal role in the diagnosis of malignant mesothelioma.

A new evaluation of worldwide studies including more than 1,800 mesothelioma patients found that people who were missing the BAP1 protein almost always had mesothelioma, while those whose cells were still producing BAP1 were not necessarily in the clear.

Understanding BAP1

The BRCA1 associated protein 1 (BAP1) gene is responsible for producing a protein (BAP1) that helps suppress the growth of mesothelioma tumors. In some people, the BAP1 gene is mutated, leading to a loss of production of the BAP1 protein. This is known as BAP1 cancer syndrome.

People with the BAP1 cancer syndrome who are exposed to asbestos are much more likely to receive a mesothelioma diagnosis than other asbestos-exposed individuals. Unfortunately, even people with intact BAP1 genes can still contract malignant mesothelioma from asbestos exposure.

The Importance of Early Diagnosis

Malignant mesothelioma, a cancer that grows on the membranes around internal organs, is extremely difficult to diagnose. It’s early symptoms such as cough and chest pain can mimic other cancers or even non-cancerous conditions.

And yet, as with most cancers, patients who are diagnosed earlier and start on aggressive treatment have a higher likelihood of surviving mesothelioma.

Although there is no definitive test for mesothelioma, the new study, conducted by researchers at the Second People’s Hospital of Hefei in Anhui, China and published in Oncotarget, suggests that BAP1 testing comes close.

Interpreting the Data

The Chinese analysis included 12 of the most recent studies of BAP1’s diagnostic value in malignant mesothelioma. All together, there were a total of 1,824 mesothelioma patient participants.

When the study data were pooled the researchers drew several important conclusions about BAP1 in mesothelioma diagnosis:

  1. BAP1 testing was more accurate when it was conducted from histological (tissue-focused) versus cytological (cell-focused) mesothelioma samples.
  2. BAP1 testing was was more effective in people with the epithelioid form of mesothelioma than it was in either biphasic or sarcomatoid mesothelioma.
  3. BAP1 was better at ruling out mesothelioma than it was at definitively diagnosing it.

“Current meta-analysis indicates that detection of BAP1 by immunohistochemical testing is a useful diagnostic marker for malignant mesothelioma,” concludes lead researcher Li-Ming Wang. “Loss of BAP1 almost provides confirming diagnosis for malignant mesothelioma, while positive staining for BAP1 is not enough to exclude non-MM.”

In other words, BAP1 testing, especially when conducted by immunohistological (IMC) means, appears to have fairly high specificity (ability to correctly identify patients without mesothelioma) but needs to be combined with other biomarkers to increase its sensitivity (ability to correctly identify patients with mesothelioma).


Wang, LM, et al, “Diagnostic accuracy of BRCA1-associated protein 1 in malignant mesothelioma: a meta-analysis”, August 17, 2017, Oncotarget

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