Smoking
harms many genes, study says BC Cancer Agency research helps explain
why many former smokers still develop lung cancer
BY
PAMELA FAYERMANVANCOUVER SUN
Sun Health Issues Reporter pfayerman@ png. canwest. com
BC CANCER AGENCY
Fibre
optic images of respiratory tracts reveal a cancer caused by smoking
in the left image.
It's
the large lumpish object blocking some of the tracts, the tube-
like structures in the lungs through which air flows when we breathe.
On the right is an undamaged lung with its tracts clear.
A
new BC Cancer Agency study serves as a sobering message why people
should never start smoking in the first place, the study’s
authors said Wednesday.
It may also help explain why so many former smokers still get lung
cancer long after they quit.
In the first study of its kind, the researchers identified a number
of genes that suffer irreversible damage from tobacco smoke, which
helps explain why half of all those diagnosed with lung cancer are
former, not current smokers.
“ Smoking is like playing Russian roulette and the longer
one smokes, the more likely it is that there will be even more bullets
in the gun,” study co- author Calum MacAulay said in an interview.
MacAulay, a biophysicist, a specialist in cancer imaging and one
of six authors of the study published Wednesday in the online journal
BMC Genomics, said it is unclear why some lifeor long- time smokers
escape lung cancer. The study didn’t delve into that.
Scientists compared samples of cells scraped from the respiratory
tracts of eight current smokers, 12 former smokers and four subjects
who have never smoked.
Using a technique called serial analysis of gene expression ( SAGE)
to help identify gene activity patterns, they identified at least
600 genes that are affected by smoking and found that while some
genes return to normal after smokers quit, about 120 genes remain
altered.
A former smoker was defined as someone who had stopped smoking for
at least a year but in the study, former smokers had quit smoking
an average of 11 years ago. The “ irreversible” changes
to their genes have persisted.
“ The former smokers in this study have a long history of
smoking ( a pack a day for 30 years or two packs a day for at least
15 years). Such irreversible damages are therefore what can happen
if an individual continues to smoke heavily for a long time,”
said Wan Lam, a molecular biologist in the agency’s department
of cancer genetics and developmental biology.
“ The longer smokers smoke, the more likely it is that genes
will be irreversibly damaged,” Lam said, adding that the study
also found that there are certain genes associated with DNA repair
that are “ irreversibly under- expressed” in people
who have smoked or still do.
Michael MacDonald, a former smoker who is a line producer in the
local film industry, said he’s not that surprised by the results.
“ I was a smoker for over 30 years,” MacDonald said,
“ and although I quit cold turkey 10 or 11 years ago, I am
not going to pretend I didn’t do permanent damage to my lungs
and I’d be very surprised if I escaped deep harm.
“ But two or three months after I quit, I felt so much better
and there’s no turning back,” he said.
“ People who smoke should realize they can’t push their
luck. Studies like this are there to forewarn and forearm,”
said MacDonald, who has enrolled himself in a lung- health study
at the cancer agency.
MacDonald, who was not in the current study, said his brother, sisters
and mother have all had brushes with cancer and his decision to
quit smoking and then get involved in research was prompted by his
family history.
He has already learned that he has a pre- malignant nodule on one
lung, he said in an interview from Los Angeles, where he is attending
business meetings.
Former and current smoking is said to account for 85 per cent of
all lung cancer cases. Lung cancer is the most common cause of cancer-
related death.
Lam said the next phase of the research will involve further study
of the role of irreversible gene changes in lung cancer development.
“ We will do this by comparing the molecular changes present
in the lung tumours from smokers versus non- smokers,” he
said. “ And we will also identify which of the changes in
the tumours are present in smoke- damaged lung tissue and absent
in normal lungs.”
One of the more surprising findings in the study was that a gene
called CABYR, which is involved in sperm motility, is more active
in smokers than in former and non- smokers.
The researchers believe this may be because smoking creates an overabundance
of mucus in the airways.
“ Over- expression” of CABYR is also found in a variety
of brain tumours.
The study was funded with g r a n t s f rom Genome Canada/ Genome
B. C., the Canadian institute of Health Research and the National
Institute of Dental and Cranialfacial Research.
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