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Study finds no link to marijuana use and oral cancer Source: (cancerfacts.com) Tuesday, June 01, 2004
SEATTLE ? June 1, 2004 ? Contrary to previous research findings that suggested a link between marijuana use and oral cancer, a new study finds no such association.
The team of population scientists led by Dr. Stephen Schwartz, of the Fred Hutchinson Cancer Research Center also found no added risk from marijuana among users who had other underlying risk factors for oral cancer, such as a history of tobacco use or heavy alcohol.
"When asking whether any marijuana use puts you at increased risk of oral cancer, our study is pretty solid in saying there's nothing going on there," Schwartz said in a prepared statement.
The study, conducted in collaboration with researchers at the University of Illinois Urbana-Champaign and Seattle's Center for Health Studies, Group Health Cooperative, involved 1,022 men and women from 18 to 65 including 407 oral-cancer cases and a comparison group of 615 healthy subjects from western Washington who were interviewed in detail about their history of marijuana use, among other lifestyle factors.
Specifically, the researchers found that marijuana users with abnormal versions of GST (gluthathione S-transferase) genes, a class of genes that produce detoxifying enzymes that help whisk toxic byproducts from the body, were at no greater risk of oral cancer than those who carry normal versions of GST.
"Our study isn't the last word on whether there are certain genetic factors that may put people who smoke marijuana at an increased risk of oral cancer, but at least with respect to GST, we didn't find any evidence that marijuana use caused a higher risk than expected in any genetic subgroups," said lead author Dr. Karin A. Rosenblatt, associate professor of community health in the College of Applied Life Studies at the University of Illinois at Urbana Champaign.
The National Cancer Institute and the National Institute of Dental and Craniofacial Research (both branches of the National Institutes of Health) funded the research, which counters findings from a smaller investigation, widely publicized in 1999. That study compared blood donors without oral cancer to patients who had been diagnosed with oral cancer at the same institution. It suggested that people who had ever used marijuana were at more than twice the risk of getting head-and-neck cancer as compared to non-users.
"Our study casts a fair bit of doubt on the overall conclusion of the previous study," said Schwartz, also a professor of epidemiology at the University of Washington School of Public Health and Community Medicine. "Blood donors tend to have fewer high-risk habits than the general population. We felt our study, which used a comparison group selected from the general population, could more accurately determine whether oral-cancer patients were more likely to have used marijuana," he said.
The study found similar marijuana-use patterns among oral-cancer cases and a healthy comparison group. The majority used marijuana less than once a week, only 1 to 2 percent of cases and controls reported smoking marijuana daily or more, and only 6 percent of cases and 4 percent of controls reported having smoked marijuana for 15 years or more.
Because the incidence of extensive, long-term marijuana use was so low among the study population ? a reflection of the population at large ? it is unclear whether extremely heavy use over many years is related to the risk oral cancer, Schwartz said.