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Archived Comments for: Analysis of aberrant methylation on promoter sequences of tumor suppressor genes and total DNA in sputum samples: a promising tool for early detection of COPD and lung cancer in smokers

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  1. Cell free DNA and methylation patterns described as a possible result of smoking frequency.

    Henry Beevers, Leeds Metropolitan University

    3 January 2013

    Due to the use of an entirely smoker free 'healthy' control group (CTR), this paper fails to distinguish between cell free DNA and methylation patterns caused by smoking, COPD and lung cancer. The increases seen in cell free DNA and increased promoter methylation of CDKN2A and MGMT could be caused by smoking as both the COPD and lung cancer groups in the study are entirely made up of smokers whilst being compared with a healthy group of non smokers, showing reduced cell free DNA and promoter region methylation.

    Either non-smoker COPD and lung cancer subjects or smoking 'healthy' subjects should have been included in order to remove the possibility that any differentiation between the groups is a direct cause of smoking which the current set of results fails to do. A possible mechanism for smoking as the cause for methylation pattern differences is shown by the authors themselves in figure 1. which shows a proposed mechanism by which tobacco NNK results in guanosine methylation.

    In addition, figure 2. has clearly been mislabeled with 'CRT' and 'EPOC as two of the groups where it should read 'CTR' and 'COPD'.

    Competing interests

    None declared