FRIDAY, May 10 (HealthDay News) -- New research says smoking pot
may be less likely to cause bladder cancer than smoking
The finding is potentially valuable, the study authors said,
given the ongoing debate over legalizing marijuana for medical
But one urologist not involved with the study was skeptical of
the finding, and noted that nonsmokers weren't among the men
included in the study.
For the study, the researchers compared the risk of bladder
cancer in more than 83,000 men who smoked cigarettes only,
marijuana (cannabis) only, or both substances. The investigators
found that men who only smoked pot were the least likely to develop
bladder cancer over the course of 11 years.
"Cannabis use only was associated with a 45 percent reduction in bladder cancer incidence, and tobacco use only was associated with a 52 percent increase in bladder cancer," said study author Dr. Anil A. Thomas, a fellow in urology at Kaiser Permanente Medical Center in Los Angeles.
Smoking both tobacco and marijuana raised the risk of bladder
cancer, but less so than for those who only smoked tobacco, Thomas
found. He presented the findings Monday at the American Urological
Association annual meeting in San Diego.
Dr. Karim Chamie, an assistant professor of urology at the David
Geffen School of Medicine at the University of California, Los
Angeles, took issue with the fact that every man in the study
smoked something, so there was no comparison to men who did not
smoke at all.
"It's hard to judge a study when the reference group is not nonsmokers," Chamie said. And the number of bladder cancers diagnosed in the study seemed low, he added, especially because everyone smoked something and smoking tobacco is considered a leading risk factor for the disease.
"We know smoking increases your risk of bladder cancer by two- or threefold," Chamie noted.
Also, the men in the study weren't representative of the entire
United States, Chamie said, noting all were insured residents of
Thomas said his research team wasn't looking at all age groups
and was not collecting data on lifetime prevalence.
Thomas stressed that he's not condoning or recommending
marijuana as a way to affect risk of bladder cancer. The value of
the study may be to spur other research into new treatments for
bladder cancer, he said.
The men in the study, aged 45 to 69, were patients at Kaiser
Permanente in California. Thomas and his team evaluated data on
their lifestyle habits, including tobacco and marijuana smoking,
between 2002 and 2003.
The researchers cross-referenced the study data with medical
records to see who was diagnosed with bladder cancer. They omitted
men with a history of bladder cancer.
Overall, 41 percent of the men reported marijuana use, 57
percent said they used tobacco and 27 percent reported using
During 11 years of follow-up, 279 men -- 0.3 percent -- were
diagnosed with bladder cancer. Eighty-nine pot smokers (0.3
percent) developed bladder cancer compared to 190 (0.4 percent) who
did not smoke pot.
More frequent marijuana use -- smoking pot more than 500 times
-- was associated with greater risk reduction than infrequent
marijuana use -- smoking once or twice, the researchers found.
Thomas said that while the study saw a link between smoking
marijuana and lower bladder cancer risk, compared to tobacco
smokers, it did not prove a cause-and-effect relationship. He
couldn't explain the link, but speculated on the possible
"The theory is that there are receptors in the bladder that are affected by cannabis," he said. The cannabinoids [compounds] in the marijuana may link with the cannabinoid receptors in the bladder and somehow protect against cell changes that can lead to cancer, he said.
A man's lifetime risk of bladder cancer is almost 4 percent,
according to the American Cancer Society. This means about one in
26 men will develop bladder tumors.
The study was funded by the Kaiser Permanente Research and
Evaluation Center. Findings and conclusions of research presented
at medical meetings should be considered preliminary until
published in a peer-reviewed journal.
To learn more about bladder cancer, visit the
U.S. National Cancer Institute.
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