Nesta your paper says there are no human studies of Carbon monoxide causing cancer. The lack of studies does not in any way mean disprove the fact Smoke causes cancer.
Clearly any study of the sort would be highly unethical / illegal in terms of exposing someone DIRECTLY to carbon monoxide in pure form.
However: carbon monoxide or not, it's known cannabis increases the risk of cancer as a matter of fact......
Cannabis smoking and lung cancer].Review article
Underner M, et al. Rev Mal Respir. 2014.
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Cannabis is the most commonly smoked illicit substance in the world. It can be smoked alone in plant form (marijuana) but it is mainly smoked mixed with tobacco. The combined smoking of cannabis and tobacco is a common-place phenomenon in our society. However, its use is responsible for severe pulmonary consequences. The specific impact of smoking cannabis is difficult to assess precisely and to distinguish from the effect of tobacco. Marijuana smoke contains polycyclic aromatic hydrocarbons and carcinogens at higher concentration than tobacco smoke. Cellular, tissue, animal and human studies, and also epidemiological studies, show that marijuana smoke is a risk factor for lung cancer. Cannabis exposure doubles the risk of developing lung cancer.
Marijuana use and risk of lung cancer: a 40-year cohort study.
Callaghan RC, et al. Cancer Causes Control. 2013.
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PURPOSE: Cannabis (marijuana) smoke and tobacco smoke contain many of the same potent carcinogens, but a critical-yet unresolved-medical and public-health issue is whether cannabis smoking might facilitate the development of lung cancer. The current study aimed to assess the risk of lung cancer among young marijuana users.
METHODS: A population-based cohort study examined men (n = 49,321) aged 18-20 years old assessed for cannabis use and other relevant variables during military conscription in Sweden in 1969-1970. Participants were tracked until 2009 for incident lung cancer outcomes in nationwide linked medical registries. Cox regression modeling assessed relationships between cannabis smoking, measured at conscription, and the hazard of subsequently receiving a lung cancer diagnosis.
RESULTS: At the baseline conscription assessment, 10.5 % (n = 5,156) reported lifetime use of marijuana and 1.7 % (n = 831) indicated lifetime use of more than 50 times, designated as "heavy" use. Cox regression analyses (n = 44,284) found that such "heavy" cannabis smoking was significantly associated with more than a twofold risk (hazard ratio 2.12, 95 % CI 1.08-4.14) of developing lung cancer over the 40-year follow-up period, even after statistical adjustment for baseline tobacco use, alcohol use, respiratory conditions, and socioeconomic status.
CONCLUSION: Our primary finding provides initial longitudinal evidence that cannabis use might elevate the risk of lung cancer. In light of the widespread use of marijuana, especially among adolescents and young adults, our study provides important data for informing the risk-benefit calculus of marijuana smoking in medical, public-health, and drug-policy settings.
PMID 23846283 [Indexed for MEDLINE]