Marijuana smoking and the risk of head and neck cancer: pooled analysis in the INHANCE consortium

Abstract

Background: Marijuana contains carcinogens similar to tobacco smoke and has been suggested by relatively small studies to increase the risk of head and neck cancer (HNC). Because tobacco is a major risk factor for HNC, large studies with substantial numbers of never tobacco users could help to clarify whether marijuana smoking is independently associated with HNC risk.

Methods: We pooled self-reported interview data on marijuana smoking and known HNC risk factors on 4,029 HNC cases and 5,015 controls from five case-control studies within the INHANCE Consortium. Subanalyses were conducted among never tobacco users (493 cases and 1,813 controls) and among individuals who did not consume alcohol or smoke tobacco (237 cases and 887 controls).

Results: The risk of HNC was not elevated by ever marijuana smoking [odds ratio (OR), 0.88; 95% confidence intervals (95% CI), 0.67-1.16], and there was no increasing risk associated with increasing frequency, duration, or cumulative consumption of marijuana smoking. An increased risk of HNC associated with marijuana use was not detected among never tobacco users (OR, 0.93; 95% CI, 0.63-1.37; three studies) nor among individuals who did not drink alcohol and smoke tobacco (OR, 1.06; 95% CI, 0.47-2.38; two studies).

Conclusion: Our results are consistent with the notion that infrequent marijuana smoking does not confer a risk of these malignancies. Nonetheless, because the prevalence of frequent marijuana smoking was low in most of the contributing studies, we could not rule out a moderately increased risk, particularly among subgroups without exposure to tobacco and alcohol.

Figure 1

The risk of head and neck cancer associated with ever marijuana smoking by study. Odds ratios were adjusted on age, sex, race/ethnicity, education level, study, packyears of tobacco smoking, years of alcohol drinking, years of cigar smoking and years of pipe smoking. Squares = study-specific odds ratios; Size of the square = the weight given to this study (inverse of the variance of the log odds ratio) when estimating the summary odds ratio; Horizontal lines = study-specific confidence intervals (CIs); Diamond = summary estimate combining the study-specific estimates with a random-effects model; Solid vertical line = odds ratio of 0.1, 0.5, 1, 2 and 10; Dashed vertical line = summary odds ratio.