Aberrant DNA methylation profile in pleural fluid for differential diagnosis of malignant pleural mesothelioma

Our plain-English summary of Aberrant DNA methylation profile in pleural fluid for differential diagnosis of malignant pleural mesothelioma, by M. Fujii, N. Fujimoto, A. Hiraki, et al (Cancer Science, 2012).

The study

• Authors: M. Fujii, N. Fujimoto, A. Hiraki, K. Gemba, K. Aoe, S. Umemura, H. Katayama, N. Takigawa, K. Kiura, M. Tanimoto, T. Kishimoto
• Journal: Cancer Science
• Published: 2012;103(3):510-4
• Cited by: 35 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma (MPM) usually develops pleural fluid. We investigated the value of DNA methylation in the pleural fluid for differentiating MPM from lung cancer (LC). Pleural fluid was collected from 39 patients with MPM, 46 with LC, 25 with benign asbestos pleurisy (BAP) and 30 with other causes. The methylation of O(6)-methylguanine-DNA methyltransferase (MGMT), p16(INK4a) , ras association domain family 1A (RASSF1A), death-associated protein kinase (DAPK), and retinoic acid receptor β (RARβ) was examined using quantitative real-time PCR. DNA methylation of RASSF1A, p16(INK4a), RARβ, MGMT and DAPK was detected in 12 (30.8%), 3 (7.7%), 11 (28.2%), 0 (0.0%) and five patients (12.8%) with MPM, and in 22 (47.8%), 14 (30.4%), 24 (52.2%), 1 (2.2%) and six patients (13.0%) with LC, respectively. The mean methylation ratios of RASSF1A, p16(INK4a) and RARβ were 0.37 (range 0.0-2.84), 0.11 (0.0-2.67) and 0.44 (0.0-3.32) in MPM, and 0.87 (0.0-3.14), 1.16 (0.0-5.35) and 1.69 (0.0-6.49) in LC, respectively. The methylation ratios for the three genes were significantly higher in LC than in MPM (RASSF1A, P = 0.039; p16(INK4a), P = 0.005; and RARβ, P = 0.002). Patients with methylation in at least one gene were 3.51 (95% confidence interval, 1.09-11.34) times more likely to have LC. Hypermethylation seemed no greater with MPM than with BAP. Extended exposure to asbestos (≧30 years) was correlated with an increased methylation frequency (P = 0.020). Hypermethylation of tumor suppressor genes in pleural fluid DNA has the potential to be a valuable marker for differentiating MPM from LC.

© 2011 Japanese Cancer Association.

In plain English

This study, from two Japanese hospitals, tested pleural fluid (fluid around the lungs) from 140 patients, collected 1996 to 2008: 39 with malignant pleural mesothelioma, 46 with lung cancer, 25 with benign asbestos pleurisy and 30 with other conditions. None of the lung cancer patients had a history of asbestos exposure. Researchers measured DNA methylation, a chemical change that can silence genes, in five genes. Three genes (RASSF1A, p16INK4a and RARb) showed significantly higher methylation in lung cancer than in mesothelioma. After adjusting for age, gender and smoking, methylation of at least one gene carried 3.51 times the odds (95% CI 1.09 to 11.34) of lung cancer rather than mesothelioma. Using a methylation ratio above 0.05 in at least one of these three genes, the test for lung cancer versus mesothelioma had 67.4% sensitivity and 79.5% specificity. Methylation levels did not differ between mesothelioma and benign asbestos pleurisy. In these asbestos-related groups, 30 or more years of asbestos exposure was associated with methylation. The authors concluded that pleural fluid methylation could be a valuable marker to help tell mesothelioma from lung cancer.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Diagnostic laboratory study comparing DNA methylation of five genes in pleural fluid across patient groups, using quantitative real-time PCR
• Who was studied: 140 patients from Okayama Rosai Hospital (114) and National Hospital Organization Yamaguchi-Ube Medical Center (26), Japan, 1996 to 2008: 46 with lung cancer (LC), 39 with malignant pleural mesothelioma (MPM), 25 with benign asbestos pleurisy (BAP) and 30 with other pulmonary diseases such as tuberculous pleurisy, empyema or simple pleurisy
• Exposure: Asbestos exposure history, taken from occupational history by questionnaire or interview for MPM and BAP patients. Table 1 gives the exposure period: median 37 years (range 3 to 50) for MPM and 32 years (range 3 to 50) for BAP. No fiber types are named. None of the LC patients had a history of asbestos exposure.
• Main results:
  • Methylation frequency of each gene was higher in malignant disease (MPM and LC) than in nonmalignant conditions (BAP and others), except for MGMT. For RASSF1A it was 40.0% versus 10.9%, P less than 0.001.
  • In MPM, the methylation profile of tumor tissue matched that of pleural fluid in 13 of 15 cases (86.7%)
  • Methylation ratios of RASSF1A, p16INK4a and RARb were significantly higher in LC than in MPM
  • For distinguishing LC from MPM, the area under the ROC curve was 0.752 (95% CI 0.661 to 0.843) at a methylation-ratio cut-off of 0.05
  • Using a methylation ratio above 0.05 in at least one of RASSF1A, p16INK4a and RARb, sensitivity was 67.4%, specificity 79.5% and positive predictive value 79.5% for diagnosing LC rather than MPM
  • In the crude analysis, the odds ratio for LC rather than MPM in patients with at least one methylated gene was 2.86 (95% CI 1.09 to 7.53)
  • After adjusting for age, gender and smoking status, the odds ratio for LC rather than MPM in patients with at least one methylated gene was 3.51 (95% CI 1.09 to 11.34)
  • Methylation ratios did not differ between MPM and BAP
  • BAP compared with other pleural diseases: the difference was statistically significant for RASSF1A (P = 0.005) but not for p16INK4a (P = 0.118) or RARb (P = 0.248)
  • In MPM and BAP patients combined (multivariate analysis), asbestos exposure of 30 years or more versus less than 30 years was associated with methylation status: odds ratio 6.393 (95% CI 1.332 to 30.688), P = 0.020
  • Among the variables in the model, the authors considered the exposure period the factor most associated with methylation status
• The authors' conclusion: The authors concluded that finding hypermethylation of RASSF1A, p16INK4a and RARb in pleural fluid DNA could be a valuable marker to help differentiate MPM from LC. As a hypothesis, they suggested that methylation in MPM and BAP may be linked to asbestos-induced chronic inflammation of the pleura.
• Limitations the authors state:
  • The authors could not explain the low rate of DAPK and MGMT methylation
  • Mesothelial cells in the pleural fluid might have interfered with detecting methylation
  • Sensitivity and specificity need improvement, through a search for genes methylated specifically in LC or in MPM

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Differential Diagnosis, Pleural Mesothelioma, Lung Cancer, Pleurisy, confidence interval, Tumor Suppressor Gene.

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