Heavy smoking is associated with increased prostate cancer (PCa) risk and higher Gleason grade among African Americans but not European Americans, according to a new study.

Among African Americans (AAs), heavy smokers (20 or more cigarettes per day) had a significant 2.6 times increased odds of a PCa diagnosis and 89% increased odds of high-grade cancer compared with never smokers or light smokers (fewer than 20 cigarettes per day), researchers reported online ahead of print in The Prostate. Heavy smoking had no significant effect on the odds of a PCa diagnosis or high-grade cancer among European Americans (EAs). This lack of an association may be due to the smaller sample size of EAs, who made up only 20.1% of cases and 28.7% of controls, the researchers observed.

The study, by Adam B. Murphy, MD, of the Feinberg School of Medicine, Northwestern University, Chicago, and colleagues included 1,085 men, of whom 527 had PCa (cases) and 558 did not (controls). Heavy smoking was less prevalent among AAs than EAs (21% vs. 30.5%).

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“Consistent with the smoking literature, we confirm that there is higher prevalence of smoking and lower prevalence rates of heavy smoking in AAs relative to EAs,” the authors concluded. “Despite these differences, we find no evidence for cigarette smoking increasing the odds of being diagnosed with prostate cancer in EA men, but are associated with prostate cancer diagnosis and high-grade disease among AA men.”

Dr. Murphy’s group pointed out some differences in smoking habits between AAs and EAs. AA men have higher plasma nicotine and metabolites than EA men even though both groups smoke the same average number of cigarettes per day, they noted. AA men have greater nicotine exposure per cigarette. This has been attributed to differences in tobacco-use behavior, including a high prevalence of menthol cigarette use, “which may confer deeper inhalation of nicotine and tobacco toxins and be associated with increased nicotine dependence.” Additionally, nicotine binds to melanin and can lead to prolonged clearance of nicotine in AA men.

Various pathways have been proposed for cigarette smoking to promote PCa tumorigenesis and progression, including an increase in bioavailable serum androgens and decrease in estradiol associated with cigarette smoking. “This would produce an environment that promotes carcinogenesis,” they wrote.