Mesothelioma or Lung Cancer? Pleural Fluid May Tell

One of the biggest challenges in treating malignant pleural mesothelioma is making a definitive diagnosis. Mesothelioma is a cancer that occurs in the membranous tissue encasing the lungs and other organs. It is almost always caused by exposure to asbestos. Although mesothelioma is not technically a lung cancer, many of its most common symptoms, such as shortness of breath and coughing, are similar to lung cancer and other lung diseases.

Like mesothelioma, many of these diseases cause a buildup of fluid around the lungs known as pleural effusion.  But there are subtle differences in the biochemical composition of that fluid from one disease to the next. A team of medical researchers in Japan is testing a new method for detecting and using some of these differences to distinguish mesothelioma from other diseases.

The team collected samples of pleural fluid from 39 patients with malignant mesothelioma, 46 patients with lung cancer, 25 with benign asbestos pleurisy (BAP) and 30 with other causes.  They then examined the fluid for methylation of the DNA.  Methylation is a biochemical process of gene expression that serves to maintain cell function throughout successive cell divisions. Alterations in DNA methlyation can be an indication of illness.

When researchers measured the methylation ratios for several key genes, they found that the ratios were much higher in patients with lung cancer than they were in patients with mesothelioma. In fact, patients with methylation in one specific gene were 3.51 times more likely to have lung cancer than any other disease. Patients who had been exposed to asbestos for 30 years or more did show an increase in the frequency of methylation, but not to the extent found in the lung cancer patients.

“Hypermethylation of tumor suppressor genes in pleural fluid DNA has the potential to be a valuable marker for differentiating malignant pleural mesothelioma from lung cancer,” concluded the study’s authors in an abstract for Cancer Science.  Using pleural fluid to confirm a mesothelioma diagnosis may offer a quicker, safer alternative to tissue biopsy.

Source:

Fujii, M et al, “Aberrant DNA methylation profile in pleural fluid for differential diagnosis of malignant pleural mesothelioma”, December 7, 2011, Cancer Science, Epub ahead of print