Article by Angela Stelmakowich, Regina Leader-Post
It appears that unlike tobacco smoking, there is no significant association between cannabis use and developing a second primary cancer, notes a new study of 500-plus patients previously enrolled at a cancer centre in Hamilton, Ont.
“The results suggest that cannabis behaves differently than tobacco smoking, as it may not be associated with the traditional concepts of field cancerization,” states the retrospective study, recently published online. Field cancerization involves the formation of patches of pre-malignant disease within the entire surface exposed to carcinogens, it explains.
“Although hypothesized, it is not yet known whether cannabis is a direct causative agent for HNC (carcinoma of the head and neck) or increases the risk of SPC (squamous cell carcinoma) through field cancerization,” the study authors write.
Conducted by researchers from McMaster University, the University of British Columbia and the University of Toronto, the study considered the outcomes of 513 patients, 59 of them in the cannabis group and 454 in the control group.
All of the patients were from the Hamilton Region Head and Neck Cancer Database and were treated at a single cancer centre between 2011 and 2015.
There were no significant difference between patients in the cannabis and control group, “except that cannabis users were more likely to develop primary oropharyngeal cancer,” notes the abstract.
Two of the 59 patients who used cannabis, 3.4 per cent, developed a second primary cancer compared to 23 of the 454 patients, 5.1 per cent, of the controls. Both of the cannabis users and six of the controls who developed an SPC were active cigarette smokers, the study states. “Eleven of the 17 non-cigarette smokers who developed an SPC were ex-cigarette smokers.”
Acknowledging the study’s limitations, the authors, nonetheless, write: “Our results are consistent with the theory that cannabis is not carcinogenic and, hence, would not follow patterns of field cancerization. Instead, it is hypothesized that since high-risk behaviours are associated with cannabis use, they may be linked to HNC through the effect of human papillomavirus (HPV) positive disease rather than a true carcinogenic property.”
Study results released by the University of California San Diego School of Medicine in early 2020 indicated how researchers believe cannabis accelerates the growth of HPV-related HNC. “HPV-related head and neck cancer is one of the fastest growing cancers in the United States. While at the same time, exposure to marijuana is accelerating. This is a huge public health problem,” professor and senior study author, Dr. Joseph Califano III, said at the time.