No Link Between Marijuana Use and Lung Cancer

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http://www.newswise.com/p/articles/view/520524/

Source: American Thoracic Society (ATS) Released: Tue 16-May-2006, 14:30 ET

Embargo expired: Tue 23-May-2006, 13:15 ET No Link Between Marijuana Use and

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People who smoke marijuana—even heavy, long-term marijuana users—do not appear

to be at increased risk of developing lung cancer, according to a study to be

presented at the American Thoracic Society International Conference on May 23rd.

Press Briefing at 10:15 a.m. (PDT).

Newswise — People who smoke marijuana—even heavy, long-term marijuana users—do

not appear to be at increased risk of developing lung cancer, according to a

study to be presented at the American Thoracic Society International Conference

on May 23rd.

Marijuana smoking also did not appear to increase the risk of head and neck

cancers, such as cancer of the tongue, mouth, throat, or esophagus, the study

found.

The findings were a surprise to the researchers. “We expected that we would

find that a history of heavy marijuana use—more than 500-1,000 uses—would

increase the risk of cancer from several years to decades after exposure to

marijuana,” said the senior researcher, Donald Tashkin, M.D., Professor of

Medicine at the David Geffen School of Medicine at UCLA in Los Angeles.

The study looked at 611 people in Los Angeles County who developed lung cancer,

601 who developed cancer of the head or neck regions, and 1,040 people without

cancer who were matched on age, gender and neighborhood. The researchers used

the University of Southern California Tumor Registry, which is notified as soon

as a patient in Los Angeles County receives a diagnosis of cancer.

They limited the study to people under age 60. “If you were born prior to 1940,

you were unlikely to be exposed to marijuana use during your teens and 20s—the

time of peak marijuana use,” Dr. Tashkin said. People who were exposed to

marijuana use in their youth are just now getting to the age when cancer

typically starts to develop, he added.

Subjects were asked about lifetime use of marijuana, tobacco and alcohol, as

well as other drugs, their diet, occupation, family history of cancer and

socioeconomic status. The subjects’ reported use of marijuana was similar to

that found in other surveys, Dr. Tashkin noted.

The heaviest smokers in the study had smoked more than 22,000 marijuana

cigarettes, or joints, while moderately heavy smokers had smoked between 11,000

to 22,000 joints. Even these smokers did not have an increased risk of

developing cancer. People who smoked more marijuana were not at any increased

risk compared with those who smoked less marijuana or none at all.

The study found that 80% of lung cancer patients and 70% of patients with head

and neck cancer had smoked tobacco, while only about half of patients with both

types of cancer smoked marijuana.

There was a clear association between smoking tobacco and cancer. The study

found a 20-fold increased risk of lung cancer in people who smoked two or more

packs of cigarettes a day. The more tobacco a person smoked, the greater the

risk of developing both lung cancer and head and neck cancers, findings that

were consistent with many previous studies.

The new findings are surprising for several reasons, Dr. Tashkin said. Previous

studies have shown that marijuana tar contains about 50% higher concentrations

of chemicals linked to lung cancer, compared with tobacco tar, he noted. Smoking

a marijuana cigarette deposits four times more tar in the lungs than smoking an

equivalent amount of tobacco. “Marijuana is packed more loosely than tobacco, so

there’s less filtration through the rod of the cigarette, so more particles will

be inhaled,” Dr. Tashkin said. “And marijuana smokers typically smoke

differently than tobacco smokers—they hold their breath about four times longer,

allowing more time for extra fine particles to deposit in the lung.”

One possible explanation for the new findings, he said, is that THC, a chemical

in marijuana smoke, may encourage aging cells to die earlier and therefore be

less likely to undergo cancerous transformation.

The next step, Dr. Tashkin says, is to study the DNA samples of the subjects, to

see whether there are some heavy marijuana users who may be at increased risk of

developing cancer if they have a genetic susceptibility for cancer.

 

 

© 2006 Newswise. .

 

 

 

 

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