The effect of smoking on the male excess of bladder cancer: a meta-analysis and geographical analyses.

Smoking is considered the primary risk factor for bladder cancer. Although smoking prevalence and bladder cancer incidence vary around the world, bladder cancer is on average 4 times more common in males than in females. This article describes the observed male-female incidence ratio of bladder cancer for 21 world regions in 2002 and 11 geographical areas during the time period 1970-1997. A meta-analysis, including 34 studies, was performed to ascertain the increased risk for bladder cancer in males and females when smoking. The summary odds ratios (SORs) calculated in the meta-analysis were used to estimate the male-female incidence ratio of bladder cancer that would be expected for hypothetical smoking prevalence scenarios. These expected male-female incidence ratios were compared with the observed ratios to evaluate the role of smoking on the male excess of bladder cancer. The male-female incidence ratio of bladder cancer was higher than expected worldwide and over time, based on a smoking prevalence of 75% in males, 10% in females and an increased risk (SOR) of bladder cancer associated with smoking of 4.23 for males and 1.35 for females, respectively. This implied that, at least in the Western world, smoking can only partially explain the difference in bladder cancer incidence. Consequently, other factors are responsible for the difference in bladder cancer incidence.