Mesothelioma is a cancer that occurs in the cells of the mesothelium, a membrane that surround the lungs and other organs. Because there are also benign conditions that can effect mesothelial cells and cause similar symptoms, mesothelioma is often difficult to identify. To date, there are no definitive biomarkers, though the list of markers that can help with diagnosis and prognosis is growing.
In the latest biomarker study, researchers in Italy evaluated BAP1 expression in 266 patients with different mesothelial conditions. A total of 212 patients had mesothelioma, 12 had benign mesothelial tumors, and 42 had been diagnosed with a condition call reactive mesothelial proliferations.
The researchers found that, while BAP1 was expressed in all of the benign tumors, well over half (66%) of the mesotheliomas were BAP1 negative, meaning the BAP1 gene was not producing the BAP1 protein. This was especially true in patients with the epithelioid or biphasic types of mesothelioma tumors. It was not the case with most of the sarcomatoid mesothelioma tumors.
The BAP1 loss proved to be especially accurate at predicting malignancy, even in cases in which biopsies had concluded that patients had reactive mesothelioma proliferation instead of mesothelioma. In all six of these cases, the patients developed mesothelioma.
The BAP1 test was also found to be highly accurate in differentiating mesothelioma from “mimickers” like lung and ovarian cancer. In the case of metastatic ovarian cancer, the specificity or percentage of people who were correctly identified as not having mesothelioma was 100%.
“BAP1 immunostain represents an excellent biomarker with an unprecedented specificity (100%) in the distinction between benign and malignant mesothelial proliferations,” advises study author and pathologist Marta Cigognetti of the University of Brescia. “Finding BAP1 loss in mesothelial cells should prompt to immediately reevaluate the patient.”
The researchers speculate that BAP1 testing might also be useful in determining the extent of a mesothelioma tumor and planning for surgery. The article appears in Modern Pathology.
Cigognetti, M et al, “BAP1 (BRCA-1 associated protein 1) is a highly specific marker for differentiating mesothelioma from reactive mesothelial proliferations”, May 29, 2015, Modern Pathology, Epub ahead of print