Risk of transitional-cell carcinoma of the bladder in first- and second-generation immigrants to Sweden

Environmental risk factors, particularly tobacco smoking, are important for transitional-cell carcinoma of the bladder. Studies in migrants may provide valuable insight into the environmental and genetic etiology of cancer. The nationwide Swedish Family-Cancer Database was used to calculate standardized incidence ratios (SIRs) for transitional-cell carcinoma among the immigrants compared with native Swedes. SIRs for lung cancer were also calculated as a proxy for smoking prevalence. Significantly decreased risks of bladder cancer were observed for male (SIR=0.89) and female (0.71) Finns and male East Asian (0.39) first-generation immigrants. Male immigrants from many countries showed increased risks, ranging from 1.18 to 2.29. Only female immigrants from Denmark (1.40) and Norway (1.27) had increased risks. The risks for bladder and lung cancers correlated, except for Finnish and Iranian men. The sons of immigrants born in high-risk countries had an increased SIR (1.51) whereas the daughters of immigrants born in low-risk countries had a decreased risk (0.32). The risk in the second-generation immigrants born in Sweden was equal to that of natives. In conclusion, the observed bladder cancer risks in the first-generation immigrants, the changes in risks in the second-generation immigrants, and the covariation of the risk patterns of bladder and lung cancers suggested a main contribution by tobacco smoking. The exceptional patterns among the Finns and Iranians may point to the existence of modifying factors. The changes in incidence in second-generation immigrants, yet based on small case numbers, lend little support to the involvement of genetic factors.