Cannabis Linked to Decreased Bladder Cancer Risk

The use of cannabis among men has been linked to a significantly decreased risk for bladder cancer, according to a recent study; however, no cause and effect association has been found.

The study, presented at the AUA 2013 Annual Meeting, found that men who reported using cannabis had a 45% lower risk for developing bladder cancer compared with men who did not smoke, even after adjusting for age, BMI, and race/ethnicity.

“Bladder cancer is one of the most prevalent genitourinary malignancies with an estimated 72,570 new cases and 15,210 cancer-related deaths per year in the United States, and it is the fourth most common malignancy in men,” Anil Thomas, MD, study author and endourology fellow at Kaiser Permanente Los Angeles Medical Center, said in an e-mail communication. “Importantly, advanced bladder cancer is inherently challenging to treat due to its associated high mortality and lack of effective systemic therapies.”

To date, there are no epidemiologic studies accurately showing what effect cannabis may have on bladder cancer. To explore the relationship further, Dr. Thomas and colleagues evaluated the incidence of bladder cancer among 82,050 men aged 45 years to 69 years enrolled in the California Men’s Health Study. All men had completed questionnaires including information on demographic and lifestyle factors such as smoking history and cannabis usage. Men who did not smoke were used as a reference group.

Results indicated that 41% of participants reported cannabis use; 57%, tobacco use; 27%, both; and 29%, neither. During the 11 years of follow-up, 279 participants (0.3%) developed bladder tumors. A significant difference was found between the number of cannabis users who developed bladder cancer and bladder cancer among men who did not report cannabis use (0.3% vs 0.4%; P < .001).

In contrast to cannabis use, which resulted in decreased risk for the disease (HR = 0.55; 95% CI, 0.31–1.00), use of tobacco was associated with an increased risk for bladder cancer (HR = 1.52; 95% CI, 1.12–2.07).

“Those using both cannabis and tobacco seemed to negate these effects with a smaller increase in their incidence of bladder cancer,” Dr. Thomas said.

After multivariate adjustment, men who reported only one or two uses of cannabis had no reduction in the incidence of bladder cancer; whereas, men using cannabis greater than 500 times had a reduction in their bladder cancer incidence hazard ratio (HR = 0.66, 95% CI, 0.36–1.21).

The researchers emphasized that the full effects of cannabis use are not known, and stated that this study is neither promoting nor condoning the use of cannabis.

“However, our findings demonstrated a reduced incidence of bladder cancer among cannabis users which could lead to further investigational studies to determine if cannabinoids, the active components of cannabis, have biologic activity against bladder cancer,” Dr. Thomas said. “Future research may eventually lead to the development of new targeted therapies for patients with bladder cancer.”