Daniel E. Ford, M.D., M.P.H. H.T. Vu, C. Hauer, K.L. Helzlsouer, J.C. Anthony Johns Hopkins University School of Medicine

Marijuana smoke contains carcinogens. Several small case series and one potentially flawed small case-control study have provided evidence that marijuana is associated with head and neck cancer. We conducted a large case-control study to address this issue. We recruited 164 participants with consecutive incident cases of head, neck, or lung cancer (adults younger than 55 years) in the Baltimore region from four hospitals between 1994 and 1999. Also recruited as controls were 526 individuals (younger than 55 years) from the Baltimore Epidemiologic Catchment Area study based on a random household sample. Cases and controls completed identical assessments of exposures via self-report, direct computer entry. Lifetime and current uses of marijuana, tobacco, and alcohol were assessed with detailed questions of use by 5- to 10-year intervals of their lives, by weekend and weekday consumption, and by mode of administration of the substance. Control patients were younger (44 vs. 49 years, p<.001), more likely to be female (62 percent vs. 34 percent, p<.001), and less likely to be white (55 percent vs. 69 percent, p<.01). Substance use was commonly reported in both cases and controls (lifetime means, 125,000 tobacco cigarettes, 27,000 alcoholic drinks, and 8,700 marijuana joints). Consistent with other studies, use of tobacco and alcohol was associated with these cancers. Ever use of marijuana (66 percent controls vs. 60 percent cases, p=.17) and lifetime marijuana joints (8,135 vs. 8,946 joints, p=.64) were not associated with cancer. Marijuana use every day for 1 month or longer also was not associated with those cancers, with or without adjustment (19 percent controls, 12 percent cases, odds ratio=.74, 95 percent confidence interval .38, 1.43). Age of first use of marijuana, depth of inhalation of marijuana, and use of pipe versus joint for marijuana were not related to these cancers. Although power was limited, marijuana use was not associated with cancer for those who never used tobacco. Adjusting for all socio-demographic factors, family history of these cancers, lifetime tobacco use, and lifetime alcohol use did not change the relationship between marijuana and cancer. The balance of evidence from this study, the largest case-control study addressing marijuana use and cancer to date, does not favor the idea that marijuana as commonly used in the community is a major causal factor for head, neck, or lung cancer in young adults.

Researchers found that smoking marijuana does not appear to increase risks of developing oral squamous cell cancers. Karin Rosenblatt, associate professor at the University of Illinois at Urbana-Champaign, said the study was undertaken to see whether data she and colleagues collected while she was working in Washington state could confirm previous studies showing a link between marijuana and oral cancer. One hospital-based study with blood donor controls found a 2.6-fold increased risk of squamous cell head and neck cancer associated with prior marijuana use (Cancer Epidemiology, Biomarkers and Prevention 1999). But no association was found in a population-based case-control study of oral squamous cell carcinoma (OSCC) in western Washington state done by investigators from the Fred Hutchinson Cancer Research Centre in Seattle. A total of 407 incident cases of OSCC diagnosed between 1988 and 1995 among persons 18 to 65 years old were ascertained from the Cancer Surveillance System of Western Washington. More than 600 matched controls were identified from the general population by random digit dialing. Data on marijuana use and established OSCC risk factors, such as cigarette smoking and alcohol use, were collected through structured in-person interviews. Dr. Karin A. Rosenblatt (PhD) said controls and OSCC cases reported nearly identical rates of having smoked marijuana (about 25% for each). There was no association with marijuana use after adjustment for sex, education, year of birth, average drinks per week, and pack-years of cigarette smoking. No increased risk was observed with increasing years of use, number of lifetime uses, number of times marijuana was used per week, years since first use, or years since last use, she reported. "Our study included about three times the number of cases and controls of the previous study and we got our controls from random digit dialing, which is the preferred population-based method. When our patients answered affirmatively to marijuana use, we asked more detailed questions," she said. *Marijuana link to oral cancers among findings new studies refute by Caroline Helwick The Medical Post Vol.37 [17] May 1, 2001