Former smokers 'still at risk of cancer', research shows

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Smoking can permanently alter the activity of genes and have irreversible effects on DNA that may be linked to cancer, research has shown.

The findings may help to explain why some former smokers contract lung cancer long after they have quit.

Scientists carried out a detailed study of cell samples from the lungs of eight current smokers, 12 former smokers and four people who had never smoked.

Libraries of DNA sequences were then constructed containing data on the activity of more than 1,700 genes.

The Canadian team found some changes in gene activity, or expression, that affected current smokers but reversed after they had quit the habit for a year or longer, according to the findings published in the on-line journal BMC Genomics.

But others appeared to be permanent, including a number that were likely to increase cancer susceptibility.

In particular, three genes associated with DNA repair had reduced activity levels in smokers which did not return to normal after they gave up the habit.

Smoking accounts for 85 per cent of lung cancers.