A study done by the new B.C. Cancer Agency and funded by the Genome Canada/Genome B.C., the Canadian Institutes of Health Research and the National Institute of Dental and Cranialfacial Research shows us why people shouldn’t start smoking in the first place and also explains why former smokers still get lung cancer long after they quit smoking.

The study authors identified a vast number of genes that suffer irreversible damage from long-term tobacco usage. This irreversible damage may be to blame why people who had quit smoking years ago still develop lung cancers.

The study didn't delve into reasons why some former smokers develop cancer and current smokers don’t. These reasons are still unclear.
What they did in their study was comparing samples of cells scraped from the respiratory tracts of eight current smokers, 12 former smokers and four people who have never smoked. By using a technique called serial analysis of gene expression (SAGE), researchers identified at least 600 genes that are affected by smoking. Further analyses showed that while some genes return to normal after quitting smoking, about 120 genes remain altered. Such irreversible damage occurs after an individual had smoked heavily for a long time. The former smokers in this study had smoked a pack a day for 30 years or two packs a day for at least 15 years. The longer smokers smoke, the more likely it is for genes to get irreversibly damaged.

Eighty-five percent of all lung cancers, the most common cause of cancer-related deaths, occur in people who are former and current smokers.

Further research will involve studying of the role of irreversible gene changes in lung cancer development. Researchers will compare the molecular changes present in the lung tumours from smokers versus non-smokers and try to identify which of the changes in the tumours are present in smoke-damaged lung tissue and absent in normal lungs.