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Malignant mesothelioma, a cancer closely associated with asbestos exposure, remains difficult to detect so researchers have been seeking new ways to help doctors identify the disease earlier and more accurately.

Japanese researchers, writing in the journal Modern Pathology, report that CD146, a protein molecule, may be a sensitive and reliable indicator of malignant pleural mesothelioma, a cancer of the lining of the lung. Once rare, the incidence of malignant mesothelioma has been increasing worldwide and is predicted to peak around 2020. More than 100,000 people die a year of mesothelioma and other asbestos-related diseases, according to the World Health Organization.

Malignant mesothelioma is resistant to conventional cancer treatment and patients typically survive 9 to 17 months after diagnosis. The poor prognosis is partly due to the fact that most cases of malignant mesothelioma are diagnosed only after the patient has an advanced stage of cancer.

The first symptoms that people with malignant pleural mesothelioma often experience are shortness of breath and/or chest pain due to excess fluid around the lungs. Doctors refer to this fluid as pleural effusions. But the symptoms often don’t appear for 30 years or more after asbestos exposure. In many cases, excess pleural fluid or hardened areas on the lining of the lung can be benign so doctors need a way to reliably distinguish between patients with malignant mesothelioma and those with non-cancerous reactions to asbestos. The researchers say analysis of chest fluid is important in patients with a history of asbestos exposure, even if they don’t show other symptoms.

The increased presence of CD146, a protein molecule, has been linked to the advanced stage of several types of malignant cancer including prostate cancer, ovarian cancer and malignant melanoma. But scientists had not previously examined the relation between CD146 and malignant mesothelioma.

For the study, the Japanese researchers examined a total of 51 cases including 23 patients with malignant pleural mesothelioma ranging in age from .44 to 92 years old, and 28 patients with excess fluid around the lung. Their research techniques involved a study of the chemical processes of immune reactions to mesothelioma at the cell level.

In the tissue samples they examined, the researchers noted that the presence of CD146 was much greater in patients with malignant mesothelioma than in patients with benign reactions involving the lining of the lung. It’s typically not present in normal mesothelial cells. Using CD146 as their indicator, the researchers were able to distinguish which patients had malignant mesothelioma in more than 90 percent of the cases they analyzed.

The researchers propose that CD146 is a reliable predictor for distinguishing malignant mesothelioma and benign mesothelial reactions.