POT USERS AT HIGHER RISK FOR HEAD, NECK CANCER, STUDY SAYS

Current and past smokers of marijuana are at increased risk of developing
cancer of the head and neck, including tumors of the mouth, throat and
larynx, a new study has found.

The study, the first to link marijuana with such cancers, suggests that the
drug's popularity in recent decades could have serious long-term health
consequences for some users. The generation of Americans who were teenagers
in the 1960s, when recreational use of marijuana became widespread, is
reaching the age when many types of cancer start to become more common.

Marijuana smoke is higher in tar and carcinogens than tobacco smoke, and
previous research has shown that marijuana smokers--like cigarette
smokers--can develop precancerous changes in cells lining the respiratory
tract. Researchers were not surprised at the news that smoking marijuana
predisposes users to head and neck cancers, and they predicted it will
likely be found to increase the risk of lung cancer as well.

"It's what I expected to see," said Li Mao, an associate professor of
medicine at M.D. Anderson Cancer Center in Houston. "It appears marijuana
[smoke] is a stronger carcinogen than cigarette smoke," said Mao, who has
followed research in the field.

Nevertheless, the independent effect of cigarette smoking on an
individual's cancer risk is probably greater than that of smoking
marijuana, noted Eugenia Calle of the American Cancer Society, "because
people just smoke so many more cigarettes."

Cancers of the mouth, throat or larynx occur in 40,400 Americans annually
and cause 12,300 deaths. Such cancers are often curable if caught early.
Smoking, chewing or sniffing tobacco, and drinking alcohol are proven risk
factors. Lung cancer is the No. 1 cause of cancer mortality, striking
171,600 Americans and killing 158,900 annually. Tobacco smoking is
estimated to cause 80% of all lung cancers.

Researchers decided to investigate the possible role of marijuana in head
and neck cancers because marijuana smoke is high in tar and people who use
the drug tend to inhale deeply, depositing four times more particulate
matter in the mouth, throat and windpipe than cigarette smokers, said
Zuo-Feng Zhang, an epidemiology professor at UCLA and a principal author of
the new study.

For the study, performed at New York's Memorial Sloan-Kettering Cancer
Center, researchers enrolled 173 patients with head or neck cancer as well
as a comparison group of 176 cancer-free blood donors of similar age and sex.

Participants were questioned about their past use of marijuana, tobacco and
alcohol, workplace and environmental exposure to possible carcinogens, and
other aspects of their background and lifestyle. Frequency of marijuana use
was categorized as never, less than or equal to once per day, and more than
once per day. Duration of use was categorized as never, one to five years
and more than five years.

Among those who had ever used marijuana, the risk of head and neck cancer
was 2.6 times greater than among those who had never used the drug.
(Researchers arrived at this figure after adjusting for the effect of other
risk factors, such as smoking and alcohol.) Researchers also observed a
dose-response effect of marijuana, with heavier users at higher cancer
risk. Among people who reported smoking marijuana once a day, the risk of
head and neck cancer was 2.1 times that of someone who never used it, while
among those who reported smoking it more than once a day, the risk was 4.9
times that of those who had abstained.

People who were current smokers of both tobacco and marijuana had by far
the highest risk of head and neck cancer, indicating that the two
substances work together synergistically to promote cancer development.
Current users of both substances had 36 times the risk of head and neck
cancer found in people who used neither.

Calle, who is director of analytic epidemiology at ACS, said the new
findings underscore the long-term danger of smoking marijuana and the need
for research into better ways of delivering the drug's active ingredients
if it is to be used by people with chronic illnesses to relieve pain,
nausea, muscle spasms and other symptoms, as some have advocated. "ACS is
supportive of research into the benefits of cannabinoids [marijuana's
active ingredients]," she said, "but . . . they do not advocate the use of
inhaled marijuana."

Calle said current and former marijuana smokers may be wise to follow
current ACS guidelines on head and neck cancer for tobacco smokers. The
society suggests smokers look for any unusual sores, lumps or patches on
lips or in the mouth, tongue, cheek or neck; ask their dentist to check the
mouth and tongue closely at each visit; and consider having a doctor
examine the mouth and neck area annually or twice a year.