[Social class differences in bladder cancer in Catalonia]

To assess the presence of socio-economic differences in bladder cancer in a heavily industrialised area of Catalonia, Spain and to evaluate risk factors associated with the presence of these differences.

218 cases and 344 population controls resident in the area of Vallès Occidental, Barcelona, were identified prospectively and interviewed during 1993-1995. Socio-economic level was evaluated through attained education and social class on the basis of the last and longest held occupation. Logistic regression was used to derive adjusted odds ratios and 95% confidence intervals.

There was no association between education and bladder cancer risk. Social class, evaluated on the basis of longest held job, was weakly related with bladder cancer, with the highest risk occurring in the highest social classes. This pattern was more pronounced when the analysis was done using the last occupation. Occupational exposures modified minimally these results. Among controls, the overall prevalence of smoking did not differ between social class but the prevalence of heavy-smokers (> 48.76 packs-year) was highest among subjects in social class V (35.5%) and lowest in social class I (10%). Adjusting for smoking enlarged social class differences.

Similarly to the pattern in other European countries, no pronounced differences by social class were observed for bladder cancer in this area of Catalonia. The evaluation of social class patterns was crucially affected by the type of socioeconomic information examined. Measures of life-time experience should be preferred rather than socio-economic level at the time of the disease. Smoking seems to be one of the main mediators for the occurrence of bladder cancer differentials but other, yet unidentified risk factors, must be associated with bladder cancer risk, especially among the highest social classes.