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Bladder Cancer Causes and Prevention: New Information from an Egyptian Study
In Egypt, bladder cancer incidence is among the highest worldwide, and the two predominant histological types of urinary bladder cancer are urothelial cell (UC) and squamous cell carcinoma (SCC), affecting roughly equal proportions of patients across the country. Cigarette smoking and occupational exposures to carcinogens have been established as risk factors for the former, whereas chronic infection with Schistosoma haematobium, which is still endemic in Egypt, is associated with the latter. Yet, these established risk factors alone cannot account for the high incidence of this malignancy, nor do they explain its disproportionate occurrence in men versus women, observed worldwide.
We investigated the associations between tobacco smoking exposure, history of schistosomiasis, and bladder cancer risk in Egypt. We analyzed data from an NIH-funded, multi-center, case-control study (1,886 newly diagnosed and histologically confirmed cases and 2,716 age-, gender-, and residence-matched, population-based controls); separately for men and women. Among the cases, 689 were SCC (35%) and 1,197 were UC (60%), and the male:female ratio was 6:1 for UC and 3:1 for SCC.
Cigarette and waterpipe smoking were prevalent among men (57% smoked only cigarettes, 13% smoked only water pipes, and 8% smoked both). Smoking was rarely reported by women; only seven reported ever smoking. However, exposure to environmental tobacco smoke (ETS) among never smokers (defined as those who never smoked a water pipe or more than 100 cigarettes in their lifetime) was rampant among both men and women (74% and 62, respectively). Among men, about half self-reported a history of schistosomiasis, compared to less than a quarter of the women.
Among men, cigarette smoking was associated with increased risk of having UC (odds ratio [OR]=1.8), but not SCC. Smoking both cigarettes and water pipes was associated with an even higher risk of UC (OR=2.9) and significant risk for SCC (OR=1.8), although the intensity (mean pack-years) was slightly lower in men who smoked both types of tobacco than in those who smoked cigarettes only.
ETS exposure among male never-smokers, both at home and outside the home, was significantly associated with a 2.5-fold increase in UC, but not SCC. Similar exposure among women was associated with increased risk that was non-statistically significant for UC (OR = 1.8, 95% CI = 0.8 to 3.8) and borderline for SCC (OR = 2.1, 95% CI = 1.0 to 4.4).
Regarding schistosomiasis, we observed that the infections were significantly associated with UC and SCC risk in both men and women, but more strongly in women.
With this large, population-based study, we provided new evidence for an association between schistosomiasis and risk of UC among non-smoking Egyptian women, and confirmed that this parasitic infection is a risk factor for SCC in both men and women. We showed a novel finding that smoking both water pipes and cigarettes increased the risk of both UC and SCC in Egyptian men, whose smoking habits are characterized by lower levels of pack-years and a large proportion of non-daily smokers, relative to men in the U.S. These findings have potentially important public health implications for Egypt and worldwide, where the prevalence of waterpipe smoking is increasing among youths, and there is a general perception that water pipe smoking is less harmful than cigarette smoking. Last but not least, our data suggested that exposure to ETS is associated with UC in both women and men, and perhaps with SCC in women. ETS has been established as a lung carcinogen by the IARC, but the evidence for its association with bladder cancer remains insufficient. Epidemiological studies have great potential to shed light on these and other important questions about bladder cancer causes and prevention.
Christopher A. Loffredo1 and Sania Amr2 as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
1Lombardi Comprehensive Cancer Center, Georgetown University, Washington DC
2University of Maryland School of Medicine, Baltimore, MD