PHILADELPHIA Lung cancer that develops in smokers is not the same disease as lung cancer that develops in people who've never touched a cigarette, a new study finds.

There are nearly twice as many DNA changes in the tumors of people who have never smoked than in the tumors of people who smoke, which suggests the cancer of "never-smokers" is different from smokers' cancer, said Kelsie Thu, a Ph.D. candidate at the BC Cancer Research Center in Canada.

"We think this finding provides evidence that never-smoker and smoker lung cancers are different, and suggests they arise through different molecular pathways," Thu told MyHealthNewsDaily. "Never-smokers might be exposed to a carcinogen, not from cigarettes , that causes their tumors to have more DNA alterations and promotes lung cancer development."

The results are in line with previous research, including a 2007 review in the journal Nature and a 2007 review in the Journal of Thoracic Oncology that suggested cancer in smokers and never-smokers arises from different mechanisms. However, the new study looked beyond mutations of a single gene, and found whole regions of DNA alterations to be different in the lung tumors of smokers compared with never-smokers.

The study was presented here today (Nov. 8) at the Frontiers in Cancer Prevention Research Conference, held by the American Association for Cancer Research.

Genomic tests

Researchers collected lung tumors and noncancerous tissue from 30 never-smokers, 39 current smokers and 14 former smokers.

They found that never-smokers had more mutations in the genes that encode molecules called epidermal growth factor receptors (EGFRs), which receive signals on cell membranes, than current or former smokers. Researchers also found more alterations in the genomes of never-smokers than the genomes of current or former smokers.

There is other evidence the lung cancers of the two groups arise from different factors, Thu said. For example, never-smokers with lung cancer are usually female, have a certain type of tumor (called adenocarcinoma) and have more mutations in their EGFRs.

But "EGFR mutations are not the only mutations driving cancer development in never smokers," Thu said, which is why she and her colleagues looked at all genes in the tumors they analyzed, to see broad regions of DNA that were different between smokers and non-smokers.

Understanding the implications

More work is required to validate the new findings, but it's possible the DNA variations found could lead to treatments designed to combat each type of cancer, Thu said.

"By improving what we know about how lung cancer develops in never smokers," she said, "our results will help us better understand the biology underlying lung cancer development in never smokers, ultimately leading to the development of better diagnostic and treatment strategies."

Next, Thu said she wants to confirm the findings by investigating the genes in other lung tumors, using datasets from other researchers. If she and her colleagues find the same DNA variation patterns, they can work to define what these genes do.