Risk of testicular cancer according to birthplace and birth cohort in Denmark.

Based on the intriguing finding of an east-west gradient of testicular cancer risk in the Nordic countries with a low risk in Finland, intermediate in Sweden, and high risk in Denmark, it was suggested that national practices rather than individual behavior may be important in the etiology of this cancer. We investigated the risk of testicular cancer in all men born in Denmark, 1931-1969 according to birthplace. Testicular cancer information was derived from the Danish Cancer Registry and population data from Statistics Denmark. There was a several fold geographical variation in testicular cancer risk within Denmark. Among men born in the early period, 1931-39, the highest risk was primarily observed in the western part of Denmark whereas no such gradient was observed in more recent cohorts. The incidence of testicular cancer increased in all counties from the earliest to the latest birth cohort, but the increase was highest in the eastern parts of Denmark. The heterogeneity in risk according to place of birth within Denmark suggests that individual behavior plays an important role for the risk of testicular cancer. Based on the Danish data, the factor that may have caused the east-west gradient in testicular cancer risk appears to have been more unevenly distributed in the early part of the past century compared to more recent times.