The impact of characteristics of cigarette smoking on urinary tract cancer risk: A meta-analysis of epidemiologic studies

Although narrative reviews have concluded that there is strong support for an association between cigarette smoking and urinary tract cancer, the association has never been quantified systematically in reviews. The purpose of this systematic review was to summarize and quantify the impact of different smoking characteristics (status, amount, duration, cessation, and age at first exposure) both unadjusted and adjusted for age and gender. The authors included 43 epidemiologic studies (8 cohort and 35 case-control) and calculated summary odds ratios (SORs) by meta-regression analyses for different smoking characteristics. They also evaluated changes in summary estimates according to differences in study methodology. Smoking status and increased amount and duration of smoking were associated with a strong increased risk of urinary tract cancer. Smoking cessation and age at first exposure were negatively associated with the risk of urinary tract cancer. The age- and gender-adjusted SORs for current and former cigarette smokers compared with those for nonsmokers were 3.33 (95% confidence interval [CI], 2.63-4.21) and 1.98 (CI, 1.72-2.29), respectively. Even though the component studies differed in methodology, the results were rather consistent. The results suggest a substantial increase in risk of cancer of the urinary tract for cigarette smokers. Based on the results of this study and previous literature, the authors conclude that current cigarette smokers have an approximately threefold higher risk of urinary tract cancer than nonsmokers. In Europe, approximately half of urinary tract cancer cases among males and one-third of cases among females might be attributable to cigarette smoking.