Stesura Seveso Archivio Italiano di Urologia e Andrologia 2022; 94, 2248 REVIEW No conflict of interest declared. on the role of Cannabis in different types of cancer have mainly focused on the oral cavity, the lungs, the gastroin- testinal tract, and genitourinary system. Upon legalization of Cannabis in Canada in October 2018, social acceptance and prevalence of Cannabis use have been rising dramat- ically in parallel with the concern about the disadvanta- geous and long-term consequences. Considering the direct exposure, bladder can be potentially impacted by Cannabis use to a considerable extent, i.e. general bladder health, and bladder cancer occurrence and prognosis (3). However, there is a scarcity of data on the link between Cannabis use and bladder cancer. To investigate the link between Cannabis use and bladder cancer, we conducted a systematic review. MATERIALS AND METHODS Study objective Study objective was to assess the association between Cannabis use and bladder cancer. It is noteworthy that the review method was established prior to the conduct of the review, from which there was no significant deviation. Search strategy A systematic literature review was performed using stud- ies published in electronic databases including PubMed, MEDLINE, and Google Scholar. Based on the Boolean search strategy, a variety of combi- nations contained the following search terms were applied in different search engines to ensure the compre- hensiveness of the result. In addition, the reference lists of the retrieved studies were manually screened. The search terms included “marijuana OR marihuana OR tetrahydro- cannabinol OR dronabinol OR cannabinoid OR Cannabis, AND bladder cancer OR bladder carcinoma OR bladder tumor OR bladder neoplasm OR urothelial carcinoma OR transitional cell carcinoma. Selection criteria We did not restrict the search with specific design, year of publication or human studies due to existing scarcity of literature on this topic. We just excluded the commentary and letter to editor. We enquired two experts in the fields to avoid missing any published or unpublished papers. Objective: To assess the association between Cannabis use and bladder cancer. Methods: A systematic literature review was performed using studies published in electronic databases including PubMed, MEDLINE, and Google Scholar. Due to the scarcity of literature on this topic, the search was not limited to a specific design, year of publication, or human studies. The studies were screened by two reviewers in the following steps; first, the stud- ies were discovered according to the predetermined search strat- egy; second, the unrelated studies and duplicates were eliminat- ed by screening the abstracts, titles, and keywords; third, the full text of relevant and eligible papers were critically appraised and assessed for the risk of bias using the respective tool. The two review authors independently assessed the risk of bias and outcome levels using the Newcastle-Ottawa Scale for the outcomes in observational studies. Any disagreements were set- tled by a third party. Results: The search strategy yielded 39 research articles. After removing 21 duplicates, 18 publications were eligible for title and abstract review. Thirteen studies were found to be irrele- vant and subsequently excluded. Only three full-text articles were evaluated and included in the qualitative synthesis. Conclusions: The role of Cannabis in bladder cancer has been seldom studied. The small number of studies show contradictory findings; potential carcinogenic versus protective effect. The growing interest in Cannabis use after legalization necessi- tates further investigations with a robust design to assess the long-term effect of Cannabis on bladder cancer. KEY WORDS: Bladder cancer; Cannabis; Cannabinoids; Marijuana; Legalization. Submitted 18 March 2022; Accepted 5 April 2022 INTRODUCTION Cannabis (also known as marijuana) is a term used to describe a vast array of products that can be produced from any part of the Cannabis sativa, Cannabis indica, or Cannabis ruderalis plants individually, or in combination. The three most common administration routes for Cannabis are smoking, vaporizing, and eating (1). When it comes to elimination, Cannabis and its byproducts pass through both the gastrointestinal and urinary tracts that can lead to a direct contact and respective responses in the corresponding organs (2). Accordingly, many studies The association of bladder cancer and Cannabis: A systematic review Vahid Mehrnoush 1, Stacy Grace de Lima 2, Ahmed Kotb 1, Matthew Eric Hyndman 3 1 Department of Urology, Northern Ontario School of Medicine, Thunder Bay, Ontario, Canada; 2 Inflammation Research Network-Snyder Institute for Chronic Disease, Departments of Physiology & Pharmacology and Medicine, University of Calgary Cumming School of Medicine, Calgary, Alberta, Canada; 3 Department of Urology, Southern Alberta Institute of Urology, Calgary, Alberta, Canada. DOI: 10.4081/aiua.2022.2.248 Summary 249Archivio Italiano di Urologia e Andrologia 2022; 94, 2 Bladder cancer and Cannabis Screening data The studies were screened by two reviewers in the fol- lowing steps; first, the studies were discovered according to the predetermined search strategy; second, the unrelat- ed studies and duplicates were eliminated by screening the abstracts, titles, and keywords; third, the full text of relevant and eligible papers were critically appraised and assessed for the risk of bias using the respective tool. Data extraction The following information was extracted from each selected study: Population characteristics, type of study, country, and key rele- vant findings. As noted, the data extraction was performed in duplicate by the two reviewers. The consensus on what informa- tion should be extracted and included was achieved. Methodological quality (R isk of Bias) The two review authors (VM and SDL) independently assessed the risk of bias and outcome levels using the Newcastle-Ottawa Scale for the outcomes in observational studies (6). Any disagreements were settled by a third party (AK and MEH). RESULTS Study selection Figure 1 depicts the PRISMA flowchart of the study selection process. The search strategy yielded 39 research articles. After removing 21 duplicates, 18 publications were eligible for title and abstract review. Thirteen studies were found to be irrelevant and subse- quently excluded. Following full-text evaluation, two papers (one commentary and one letter to the editor) were excluded. Only three full-text articles were evaluated and included in the qualitative synthesis. Table 1. Summary of clinical studies on Cannabis and bladder cancer. Figure 1. PRISMA flowchart of the results of the literature search. Author Study design Country Population Intervention/Exposure Comparator Outcome ROB Chacko et al. 2006 (4) Case control USA 124 Patients with Use of marijuana Age-matched control A history of habitual marijuana use in 88.5% and 69.2% Moderate bladder cancer of transitional cell carcinoma patients and age-matched controls, respectively (p = 0.008). The association between marijuana use and tumor stage, grade, and number of recurrences of transitional cell carcinoma. Thomas et al. 2015 (5) Cohort USA 84170 Participants Cannabis users Not reporting Cannabis Incident bladder cancer 0.3% among Cannabis users versus Moderate in a multiethnic use 0.4% among men not reporting Cannabis use (p < .001). cohort of men aged Cannabis use associated with a 45% reduction 45-69 years in bladder cancer incidence (HR, 0.55; 95% CI, 0.31-1.00). Nieder et al. 2006 (11) Case report USA 1 Case Use of marijuana NA Inhaling up to five marijuana cigarettes per day NA with bladder cancer for 30 days as the only risk factor for transitional cell carcinoma. ROB: Risk of bias. NA: Not applicable. Archivio Italiano di Urologia e Andrologia 2022; 94, 2 V. Mehrnoush, S.G. de Lima, A. Kotb, M.E. Hyndman 250 Included studies characteristics Three studies with moderate risk of bias (mainly due to limited information regarding the average marijuana expo- sure and inadequate adjustment for key confounders) were included for review. Table 1 shows the specific details of each. DISCUSSION Cannabinoids have been shown in studies to inhibit tumor cell growth and induce apoptosis in a variety of cancer cells (5-7). Despite widespread Cannabis use and evidence of cannabinoids' antitumor activity, little is known about the carcinogenic effects of Cannabis, which has been highlighted after Cannabis legalization. The find- ings on the effect of Cannabis on other urinary malignan- cies vary. The only clinical study on penile cancer and Cannabis found no link (7). Cannabis use appears to be an independent risk factor for the development of testicular germ cell tumors (9-11). The result of a study on the effect of Cannabis on prostate cancer did not find a link between Cannabis and prostate cancer risk (8); however, in vitro and animal studies strongly suggest that cannabinoids protect against prostate cancer development (9). The clinical studies on renal cancer merely characterized cannabinoid receptor expression in renal neoplasms (10). Two studies yielded contradictory results on Cannabis and bladder cancer according to our review. Chacko et al. compared 52 men under the age of 60 with transitional cell urothelial carci- noma to 104 age-matched controls. Their findings revealed that habitual marijuana use was present in 88.5% of patients with bladder cancer while 69.2% of the control group (p = 0.008), implying that marijuana use is associated with an increased risk of blad- der cancer (4). This is consistent with the findings of a case report of 45-year-old man in whom excessive mari- juana smoking (up to five marijuana cigarette daily more than 30 years was found to be the only risk factor for developing bladder cancer (11). A recent study by Thomas et al., which examined the records of 84170 men aged 45-69 years from the California Men's Health Study and followed them for 11 years, discovered that bladder cancer developed in 0.3% of men who used Cannabis and 0.4% of men who did not use Cannabis (p = 0.001), leading the authors to conclude that Cannabis use was associated with a 45% risk reduc- tion in the bladder cancer incidence (5). However, the studies were limited by insufficient adjustment for con- founders. Knowing the physiology of the tissue expression of cannabinoid receptors can shed more light on the poten- tial role of Cannabis in bladder cancer. Tyagi et al. found CB1 and CB2 receptors in the urothelium of human blad- der (12). Both receptors were present in the bladder urothelium and detrusor muscles, but CB1 expression was found to be significantly higher than CB2. CB1 and CB2 receptor expression was twice as high in urothelium as it was in detrusor muscles (12). Cannabis has primari- ly been studied in terms of regulating inflammation and urgency in the treatment of bladder conditions. CB2 ago- nists have been shown to reduce the severity of murine bladder inflammation when locally administered after acrolin, an inflammatory agent (13). As part of the Cannabinoids in Multiple Sclerosis (CAMS) study, Freeman et al. investigated the effect of cannabinoids on urge incontinence. They assigned 630 patients with multiple sclerosis to receive either Cannabis extract, THC, or a matched place- bo via oral administration. Urge incontinence was signif- icantly reduced with Cannabis (38%), and THC (33%), versus placebo (18%) (14). Kavia et al. also found that Sativex (THC + cannabidiol) can also a positive impact on overactive bladder symptoms in patients with multiple sclerosis (15). The existing small body of evidence indicates that Cannabis has a direct effect on the bladder during elimi- nation where the resulting direct contact with the bladder urothelium can cause change in urine peptides and urothelial expression of CB1 and CB2 receptors. Although it is currently difficult to study Cannabis's effects on the bladder, legalization may increase this pos- sibility due to the increased openness of the population regarding their use of Cannabis. Because of the long laten- cy nature of bladder cancer development, more robustly designed studies with long-term follow-up are warranted. Given the gaps in current knowledge, the authors pose the following dire questions for future observation and study: Will Cannabis reduce or increase the incidence of BC? Will Cannabis influence BC aggression in a positive or negative way? Will new pathological types of BC emerge? Many questions may arise, but only observation and ongoing research will allow us to begin finding true, con- clusive evidence. CONCLUSIONS The role of Cannabis in bladder cancer has been seldom studied. The small number of studies show contradictory findings; potential carcinogenic vs protective effect. The growing interest in Cannabis use after legalization necessitates further investigations with a robust design to assess the long-term effect of Cannabis on bladder cancer. REFERENCES 1. Russell C, Rueda S, Room R, et al. 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Randomized controlled trial of Sativex to treat detrusor overactivity in multiple sclerosis. Mult Scler. 2010; 16:1349-59. Correspondence Vahid Mehrnoush, MD vahidmehrnoush7@gmail.com Department of Urology, Northern Ontario School of Medicine Thunder Bay, Ontario (Canada) Stacy Grace de Lima, BSc stacy.ggibson@gmail.com Inflammation Research Network-Snyder Institute for Chronic Disease, Departments of Physiology & Pharmacology and Medicine, University of Calgary Cumming School of Medicine, Calgary, Alberta (Canada) Ahmed Kotb, MD, FRCSC (Corresponding Author) drahmedfali@gmail.com Northern Ontario School of Medicine TBRHDC, 980 Oliver Road Thunder Bay, Ontario (Canada) P7B 6V4 Matthew Eric Hyndman, MD, FRCSC (Corresponding Author) erichyndman@shaw.ca Southern Alberta Institute of Urology, 7007 14 Street SW, Calgary, AB, Canada. T2V 1P9