Does smoking marijuana increase the risk of head and neck cancers?

Clinical records over two decades

Cannabis is currently the most commonly used illegal drug worldwide. HNC currently represent the sixth most common type of cancer. The authors of the study, a team of experts from the USC Head and Neck Center in Los Angeles, aimed to obtain the most valid results regarding the relationship between cannabis use and HNC, which was reflected in the size and composition of the study sample. They drew from clinical records stored in a database containing data from 64 health organizations collected over 20 years (until April 2024), covering more than 90 million individuals.

In this database, researchers looked for medical records of adult Americans who visited a hospital clinic, whether they had a cannabis use-related disorder or not, and had no history of HNC. Using propensity scores, they created 2 groups of individuals with corresponding demographic characteristics, occurrences of alcohol-related disorders, and tobacco use.

New HNC cases were monitored from 1 to 5 years. They calculated the relative risk of developing HNC and its specific locations in individuals with a cannabis use-related disorder compared to those without this disorder. Additionally, the analysis was performed separately for individuals under 60 years old and those aged 60 and older.

Higher incidence of HNC associated with cannabis use

The disorder related to cannabis use was found in 116,076 individuals with an average age of 46.4 years (44.5% women). The cohort without a cannabis use-related disorder consisted of 3,985,286 individuals with an average age of 60.8 years (54.5% women). After creating matching cohorts according to propensity scores, each consisted of 115,865 individuals.

The risk of a new HNC diagnosis was significantly higher in individuals with a cannabis-associated disorder, at 3.5 times (RR 3.49; 95% CI 2.78–4.39). A higher risk in the cohort with a cannabis use-related disorder was found in all individual HNC locations, with a 2.5 times higher risk for oral cavity carcinoma (RR 2.51; 95% CI, 1.81–3.47), 5 times for oropharyngeal carcinoma (RR 4.90; 95% CI, 2.99–8.02), and more than 8 times for laryngeal carcinoma (RR 8.39; 95% CI 4.72–14.90). The results were consistent in both older and younger age groups.

The harmful effects of smoke

The primary reason why cannabis increases the risk of HNC, according to the study authors, is the harmful effect of smoke, as the most common method of cannabis consumption is inhalation (although the study did not differentiate between methods of use). The mechanism may be similar to that of tobacco smoking, whose smoke contains numerous chemicals that cause DNA damage and inflammation, which can lead to malignant growth.

With cannabis smoke, it could be similar, or even worse. Such evidence was suggested by Dr. Niels Kokot, a head and neck surgeon and one of the main authors of the study. "Cannabis smoke is usually unfiltered, and its inhalation is deeper compared to tobacco smoke. Additionally, cannabis burns at a higher temperature than tobacco, which increases the risk of inflammation causing malignancies," he stated.

What next?

According to Dr. Kokot, the study conducted by his team is one of the first to show a link between HNC and cannabis use, and it is the largest so far. Future research should focus on exploring the mechanisms of this association and analyze the effect according to dose size, thus obtaining more detailed evidence about cannabis use as a risk factor for the development of HNC.

Editorial Team, Medscope.pro

Sources:

1. Gallagher T. J., Chung R. S., Lin M. E. et al. Cannabis use and head and neck cancer. JAMA Otolaryngol Head Neck Surg, 8. 8. 2024, doi: 10.1001/jamaoto.2024.2419.
2. Keck Hospital of USC. Cannabis use tied to head and neck cancer. Press release, 8. 8. 2024. Available at: www.news.keckmedicine.org/cannabis-use-tied-to-head-and-neck-cancer