New study discounts link between oral cancer, pot smoking

  1. Wednesday, June 2, 2004

    New study discounts link between oral cancer, pot smoking
    Previous research found a correlation


    Smoking marijuana does not increase the risk of developing oral cancer, according to a new study from Seattle researchers that contradicts an earlier study.

    The previous study, led by researchers from the University of California-Los Angeles in 1999, found that marijuana users were 2.5 times more likely to develop head and neck cancer, including tumors of the larynx and throat, than non-users. Researchers suggested that baby boomers who began smoking marijuana during the 1960s, when the drug surged in popularity, could experience higher rates of head and neck cancers as they age.

    But the latest research finds no indication of an elevated risk, said Stephen Schwartz, an epidemiologist at the Fred Hutchinson Cancer Research Center and the new study's lead author. More than three times the number of participants were included in the latest study, improving the reliability of the findings, Schwartz said.

    "If people are thinking about what might be happening to them in the future because of marijuana use, oral cancer is not something you should be particularly worried about," said Schwartz.

    The study, published in the June issue of Cancer Research, the journal of the American Association for Cancer Research, included 407 people with oral cancer and 615 healthy adults between ages 18 and 65 from King, Pierce and Snohomish counties, who were located using random telephone surveys.

    Participants were asked to describe their marijuana use between 1985 and 1995, including how often they smoked. About 25 percent of participants in both groups said they had smoked marijuana at some point in their lives.

    Marijuana use has also been linked to lung cancer, with studies indicating that marijuana smoke can cause molecular and cellular changes in lung tissue that are consistent with the early stages of cancer. Marijuana smokers inhale more deeply and hold the smoke in their lungs longer than tobacco smokers, which may explain the high levels of tar found in marijuana users' lungs. In addition, marijuana cigarettes do not have filters.

    An estimated 28,260 new cases of oral cancer will be diagnosed this year nationwide, resulting in 7,200 deaths, according to the American Cancer Society. Cigarette smoking, chewing tobacco and alcohol are all known risk factors for oral cancer, which is found most commonly on the tongue, but also appears on the lips, floor of the mouth and tonsils.

    Because so few of the study participants said they were chronic, long-term users, it's unclear whether frequent marijuana use could lead to oral cancer, Schwartz said.

    Dr. Zuo-Feng Zhang, an epidemiology professor at the Jonsson Cancer Center at UCLA, led the 1999 study and is nearly finished with a larger study involving about 2,400 people. His research, looking at the connection between head, neck and lung cancer and marijuana use, is funded by the National Institute on Drug Abuse.
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