CHAMPAIGN, Ill. – Oral cancer probably hasn’t been high on the average pot smoker’s list of concerns – despite the fact that marijuana smoke contains known carcinogens. It may be even less of a concern now in light of new research that found no link between marijuana use and risk of developing oral squamous cell carcinoma (OSCC).
The research results, which diverge significantly from those of previous investigations, were based on a large, population-based case-control study conducted by collaborating researchers from the University of Illinois at Urbana-Champaign and Seattle’s Fred Hutchinson Cancer Research Center and Center for Health Studies, Group Health Cooperative. Their findings – the most comprehensive to date regarding possible connections between marijuana use and OSCC – were reported in the June issue of Cancer Research, a publication of the American Association for Cancer Research.
“We did not see an increase in risk for oral cancer in people who had ever smoked marijuana after controlling for other risk factors, such as tobacco smoking and alcohol consumption,” said Karin Rosenblatt, a cancer epidemiologist and professor of community health at Illinois. Rosenblatt, a lead researcher on the project, noted that the study’s findings were consistent, regardless of variable patterns of marijuana use, including how much individuals smoked, how often and for how long.
“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,” said Stephen M. Schwartz, the study’s senior author. Schwartz is a member of Fred Hutchinson’s Public Health Sciences Division and a professor of epidemiology at the University of Washington.
The study results run counter to those found in previous investigations, including case reports and a widely publicized hospital-based case-control study, issued in 1999, which suggested marijuana users’ chances of developing head-and-neck squamous-cell carcinoma were more than twice that of non-users.
“The main problem (with that study) was that the control group was blood donors,” Rosenblatt said. Such individuals aren’t typically representative of the population at large, she said, because “they are screened for HIV and tend not to have certain drug or sexual habits that put them at greater risk for contracting infectious diseases.”
The size of the new study’s data pool – three times that of the 1999 study – also makes it more statistically viable. Additional attributes include the collection of more detailed data about participants’ marijuana use, and inclusion of a greater number of subjects who reported using the drug for five or more years.
As epidemiologists – public-health professionals interested in the cause and distribution of diseases among populations – the study’s authors said a number of factors motivated them to pursue a broader investigation of possible links between marijuana use and oral cancer. Among them, they cited a general concern that “marijuana is the most commonly used illegal drug in the United States, and new users increased among minors during the 1990s.”
Further concerns included indications from experimental studies that “components of marijuana smoke are mutagenic in bacteria and cause molecular and cellular changes in bronchial tissue comparable to those seen among tobacco smokers and consistent with early steps in cancer development.”
The new study, funded by the National Institutes of Health’s National Cancer Institute and National Institute of Dental and Craniofacial Research, focused on marijuana-use histories and other lifestyle habits of 407 oral-cancer cases and 615 healthy control subjects from western Washington. Research subjects included males and females aged 18 to 65.
The oral-cancer cases were drawn from a registry, based at Fred Hutchinson, which is part of the National Cancer Institute’s Surveillance, Epidemiology and End Results program. General-population participants were selected through random-digit telephone dialing.
Similar marijuana-use patterns were found among both groups studied – 25.6 percent of case subjects and 24.4 percent of control subjects reported ever using marijuana or hashish. Most reported using it less than once a week, with 2 percent or less reporting daily use. Six percent of case subjects and 4 percent of controls had smoked marijuana or hashish for 15 years or more.
In addition to analyzing and comparing data obtained through in-person interviews, the researchers analyzed publicly available data from the National Household Survey of Drug Abuse, collected over several years, and obtained biological specimens from participants.
Through analysis of the biological specimens, Rosenblatt and her colleagues further determined that marijuana users with defective GST (gluthathione S-transferase) genes were not exposed to greater risks for oral cancer than counterparts with normal GST genes. GST genes, Rosenblatt noted, produce enzymes that aid in the body’s detoxification process.
