RESEARCHERS LINK MARIJUANA TO CANCER

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 said they therefore 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, who has followed
research in the field. "It appears marijuana [smoke] is a stronger
carcinogen than cigarette smoke."

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 (ACS), "because people just
smoke so many more cigarettes."

Researchers have estimated that 31 percent of Americans who were over 11
years old in 1992 have tried marijuana. However, Mao said, few studies have
examined marijuana's impact on long-term cancer risk. He added that because
the drug is illegal, it is more difficult to get people to be honest about
their past marijuana use than about their cigarette-smoking history.

"It probably will be much harder than [with] cigarette smoking to prove" a
link between marijuana and lung cancer, Mao said.

Cancers of the mouth, throat or larynx occur in 40,400 Americans annually
and cause 12,300 deaths. Cancers in these areas are often curable if caught
early. Smoking (of cigarettes, pipes or cigars), chewing or sniffing
tobacco, and drinking alcohol are proven risk factors.

Lung cancer is the number one cause of cancer mortality, striking 171,600
Americans and killing 158,900 annually. Tobacco smoking is estimated to
cause 80 percent of all lung cancers. Asbestos, radon and occupational
exposure to certain carcinogens are also recognized risk factors.

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, a professor of epidemiology at the University of California
at Los Angeles School of Public Health and principal author of the new
study. "If marijuana smoking has anything to do with smoking-related cancer,
the oral cavity would be the first site being affected," he said.

For the study, performed while Zhang was working 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. All study 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.) They also observed a
dose-response effect of marijuana, with heavier users at higher cancer risk.
Among people who reported smoking marijuana once per 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 per day, the risk was 4.9 times
that of those who had abstained.

Furthermore, 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."

Should current or former marijuana smokers have special checkups?
Considering the new findings, Calle said, they might be wise to follow
current ACS guidelines on head and neck cancer for tobacco smokers. The
society suggests that smokers stay on the lookout for any unusual sores,
lumps or patches on lips or in the mouth, tongue, cheek or neck; ask their
dentist or dental hygienist 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.