Geographical Pattern of Testicular Cancer Points to Maternal Exposures Behind Increasing Incidence

Evidence suggests that testicular cancer (TC) originates from germ cell neoplasia in situ arising during fetal development, implying that prenatal environmental exposures may influence disease risk. We investigated whether maternal place of residence during pregnancy is associated with regional variation in TC incidence. We conducted a nationwide cohort study including 1,342,996 men born in Finland between 1960 and 1999. Participants were followed from birth until diagnosis of TC, death, emigration, or the end of follow-up (2021). A total of 2976 TC cases were identified. Information on municipality of birth was used as a proxy for maternal residence during pregnancy. Incidence rates and cumulative incidence were estimated by birth cohort and age at diagnosis. To examine regional variation, cumulative TC incidence by birth cohort and municipality was modeled using Bayesian hierarchical binomial regression allowing incidence to vary across municipalities. TC incidence increased across birth cohorts, peaking among men born in 1975-1979 (16.8 per 100,000). Cumulative incidence rose in all municipalities, ranging from 67.9 to 132.5 per 100,000 among men born in 1960-1969 and from 283.2 to 327.6 among those born in 1980-1989. Marked geographic clustering was observed. Incidence was consistently elevated among men born in southwestern Finland and remained high throughout the study period. Over successive birth cohorts, an eastward shift in higher incidence was observed. Although direct cohort evidence linking specific environmental exposures to TC remains limited, these findings support the hypothesis that prenatal environmental factors contribute to the pathogenesis of TC and may partly explain regional differences in incidence.