NEW YORK, Dec 27 (Reuters Health) -- People who smoke marijuana may be
more likely than those who do not smoke to develop cancer of the head and neck,
according to a report in the December 17th issue of Cancer Epidemiology
Biomarker and Prevention.
"Many people may think marijuana is harmless, but it's not," said study
author Dr. Zuo-Feng Zhang, in a statement issued by the University of
California, Los Angeles.
The more often each day a person smokes marijuana, and the longer they
continue to smoke it, the greater their chance of developing cancer in places
such as the mouth, tongue, larynx or pharynx, according to the study by Zhang,
of UCLA's Jonsson Comprehensive Cancer Center, and colleagues.
The researchers compared marijuana, alcohol and tobacco use in 173
patients who had cancer of the head and neck with that of 176 blood donors who
did not have cancer.
When they eliminated other factors that contribute to cancer, including
smoking and alcohol intake, they found that people who smoked marijuana at any
point during their lifetime were 2.6 times more likely to develop head and neck
cancer compared with people who had never smoked marijuana.
The risk increased in relation to the amount of the drug used and the
number of years a person smoked marijuana. "If you smoke a little, your risk
increases a little," Zhang said. "If you smoke a lot, your risk increases a
lot."
Marijuana may interact with a genetic susceptibility to such cancers, with
cigarette smoking, and, to a lesser extent, with alcohol consumption to increase
a person's chances of developing head and neck cancer, according to the report.
Back in the 1960s, many people in their twenties smoked marijuana, Zhang
points out. Because cancers of the head and neck take 20 to 30 years to develop,
individuals who smoked large amounts of marijuana 20 to 30 years ago may just
now be developing head and neck cancer.
The researchers note that the blood donors, the comparison group in the
study, may have been less likely than the cancer patients to have used
marijuana. Or it is possible that the cancer patients were more likely than the
blood donors to remember and report marijuana use. Either factor could bias the
study, which should be confirmed with more research, the research team says.
Although it's known that the cancer-causing properties of marijuana smoke
are similar to those of cigarette smoke, this is the first study in which
investigators have looked at the relationship between smoking marijuana and head
and neck cancer, Zhang said.
It is estimated that approximately 31% of adults in the United States use
marijuana.
