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Excessive use of cannabis was associated with a higher risk of head and neck cancer (HNC), a large multicenter cohort study showed.

After matching for demographic characteristics, alcohol-related disorders, and tobacco use, patients with cannabis-related disorder had an increased risk of any HNC compared with those without cannabis-related disorder (relative risk [RR] 3.49, 95% CI 2.78-4.39), reported Niels C. Kokot, MD, of the University of Southern California in Los Angeles, and colleagues.

Moreover, a site-specific analysis showed that those with cannabis-related disorder had a higher risk of oral (RR 2.51, 95% CI 1.81-3.47), oropharyngeal (RR 4.90, 95% CI 2.99-8.02), and laryngeal (RR 8.39, 95% CI 4.72-14.90) cancers, they noted in .

"The possibility of an association between cannabis use and HNC has substantial public health implications given that cannabis use is rising among young adults with trends toward legalization," wrote Kokot and colleagues. "Future studies should seek to use similarly large cohorts to analyze the association between cannabis use and HNC but can demonstrate additional strength of the association by using more thorough data on cannabis use, including dosage, frequency, and method of use."

In a Joseph Califano, MD, of the University of California San Diego, and colleagues, pointed out that the association between tobacco carcinogens and cancer was long suppressed by the tobacco industry. Thus, they suggested this study raises the question -- "are we repeating the same mistakes of the past we made with smoking, only now with marijuana and cannabis?"

"Given that cannabis is now a $20 billion industry in the U.S. alone with expanding availability, use, and popularity, this may be 'déjà vu, all over again' without appropriate research to understand the potential carcinogenic and salutatory effects of cannabis," they wrote. "Or, in the words of Yogi Berra, 'If you don't know where you are going, you might wind up someplace else.'"

For this analysis, Kokot and colleagues used the U.S. Collaborative network to access 20 years of data from 64 healthcare organizations (accounting for more than 90 million individuals).

The cohort with cannabis-related disorder -- defined as excessive use of cannabis with associated psychosocial symptoms, such as impaired social and/or occupational functioning -- included 116,076 individuals (mean age 46.4 years, 44.5% women) who received a diagnosis of cannabis-related disorder and had a recorded outpatient hospital clinic visit and no prior history of HNC. The non-cannabis cohort included 3,985,286 individuals (mean age 60.8 years, 54.5% women) who had a recorded outpatient hospital clinic, never received a diagnosis of cannabis use disorder, and had no history of HNC.

After propensity score matching, each cohort included 115,865 individuals.

When evaluating only adults ages 60 and younger, those with cannabis-related disorder had a higher risk for any HNC (RR 3.44, 95% CI 2.32-5.10), as well as laryngeal cancer (RR 2.60, 95% CI 1.25-5.39), oral cancer (RR 2.00, 95% CI 1.19-3.38), and oropharyngeal cancer (RR 3.40, 95% CI 1.68-6.88).

Higher risks were also observed for those ages 60 and older with cannabis-related disorder:

• Any HNC (RR 3.21, 95% CI 2.44-4.21)
• Laryngeal cancer (RR 6.92, 95% CI 3.78-12.67)
• Oral cancer (RR 2.46, 95% CI 1.66-3.64)
• Oropharyngeal cancer (RR 3.28, 95% CI 1.94-5.57)

Kokot and colleagues also found that when cases of HNC were limited to those occurring more than 1 year after a cannabis-related disorder diagnosis, many of the associations increased, "demonstrating additional strength in the association."

In cases occurring 5 or more years after a cannabis-related disorder diagnosis, those associations fell in magnitude, "although several of the associations, including between cannabis use and any HNC, oral cancer, oropharyngeal cancer, and laryngeal cancer, remained," they noted.

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