Subtype-specific risk of testicular tumors among immigrants and their descendants in Sweden, 1960 to 2007.

BACKGROUND Testicular cancer is the most common cancer among young male adults in several populations. We compared subtype-specific risk of testicular cancer among migrants and their descendants to that of Swedish-born men to elucidate importance of genetic and environmental factors in testicular cancer etiology and the potential timing of exposures. METHODS We followed a nationwide cohort of 3.6 million men ages 15 to 54 years between 1960 and 2007 through linkage between Swedish National Registers. Incidence rate ratio (IRR) adjusted for age and calendar year with 95% confidence intervals (CI) was estimated using Poisson regression. RESULTS A total of 5,801 cases of testicular cancer occurred during 80 million person-years of follow-up. Compared with Swedish-born men, first-generation immigrants from low-risk countries had a lower risk (IRR, 0.43; 95% CI, 0.38-0.49) and first-generation immigrants from high-risk countries had a higher risk (IRR, 1.61; 95% CI, 1.42-1.83) of testicular cancer. The risk among first-generation immigrants varied remarkably by birthplace, reflecting the risk in their countries of birth. The risk of seminomas was statistically significantly modified by age at immigration and duration of residence among immigrants born in high-risk areas. We observed a statistically significantly convergence of risk among second-generation immigrants toward the risk in Sweden (IRR, 1.02; 95% CI, 0.93-1.12). The risk among second-generation immigrants was not affected by the duration of stay of their mothers in Sweden before pregnancy. CONCLUSIONS Our study provides evidence that life-style and environmental factors play an important role in the etiology of testicular cancer.