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Mutant genes in smokers tied to cancer |
CHICAGO: Heavy smokers who get lung
cancer may have tens of thousands of genetic mutations, US researchers said.
A team at Roche's biotechnology unit Genentech in California
compared all the genetic changes in a single patient's lung tumor with healthy
tissue from the patient, a 51-year-old man who had smoked an average of 25
cigarettes per day for 15 years before the tumor was removed.
What
they found were as many as 50,000 genetic mutations. "Fifty thousand is a huge
number. No one has ever reported such a high number," said Zemin Zhang of
Genentech, whose findings appear in the journal Nature. "This is likely
associated with the smoking history of the patient. It is very alarming," Zhang
said in a telephone interview said on Wednesday.
Smoking is the
biggest single cause of lung cancer, and studies suggest mutations occur with
each cigarette smoked.
Zhang said the ratio between the number of
cigarettes the person smoked before his tumor was removed and the number of
mutations in the tumor suggest that for every three cigarettes he smoked, one
genetic mutation occurred.
"It's a lot more complicated than that,"
Zhang said, noting that there are DNA repair mechanisms in the body that help
protect against the damage of smoking, but these become less efficient over
time.
Zhang said the team was so surprised by the findings they made extra
checks to see if they got it wrong. They also looked for anything unusual about
the smoker whose tumor they studied. "There is nothing unusual about this
sample," he said.
The findings may be sobering for those
contemplating taking up smoking. "If you imagine over a lifetime you are going
to develop this many mutations in the genome, some people may think twice about
it," he said.
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