In the United States incidence rate patterns by racial ethni
In the United States, incidence rate patterns by racial/ethnic group were similar to international patterns. In the pediatric age group, the highest incidence rates were observed in Hispanic and API children (3.5 and 2.9 per million, respectively) followed by non-Hispanic white (2.3 per million) and black (1.7 per million) children (Fig. 2). In AYA, non-Hispanic whites had the highest rates, followed by Hispanics, API and blacks, respectively. A similar distribution was observed when we evaluated the main histologic subtypes of testicular cancer in the AYA group. Rates of seminoma and non-seminoma were similar in non-Hispanic whites and API. Hispanics had a higher relative incidence of non-seminoma, while blacks had a higher rate of seminomas (Supplementary Table 1). The peak age at incidence occurs in the 25–29 year age group for Hispanics and API, while non-Hispanic whites and blacks have a peak incidence between 30–34 years (Supplementary Table 3).
Discussion This is the first comparison of international incidence rates for testicular cancer to include a wide range of countries in young boys and adolescents/young adults. When we compared incidence rates by region, we found that AT13387 regional rates for testicular cancer are similar in Europe, Oceania and North America while Asia and South America have a distinct incidence profile. Specifically, Asia had one of the highest pediatric testicular cancer rates while AYA rates were lower than other regions. Despite the differences in relative incidence rates by geographic region, age-specific incidence rates for testicular cancer followed a similar pattern in all areas with an initial peak shortly after birth followed by a decline to almost zero and subsequently followed by a second larger peak corresponding with puberty that continued into young adulthood. The change in trends at age 9 could be due to rising hormone levels that accompany puberty , which would be supported by evidence that later age at puberty is associated with a reduced risk of testicular cancer in adults . In the pediatric age group, there is a 6.5 fold variation in the incidence rate from the registry with the highest incidence rate to the lowest incidence rate. This is in contrast to the 25-fold variation in the AYA age group. A previous analysis of a more limited number of international registries also reported on the smaller scale of incidence rate variation in the pediatric age range compared with young adults . These data support differing etiology of testicular cancer in children compared with adolescents and young adults. Previous comparisons of testicular cancer incidence in young adult men have shown that northern European countries and non-Hispanic white men in the United States have the highest testicular cancer rates in the world [5,6,, , , , ]. While we did observe the highest regional rates in Europe in the AYA age group, there was considerable variation within the region. Rates for API AYA in the United States, while still low, are higher than rates in Asia overall, at 37.1 compared to 27.1 per million. Of the etiologic factors that have been evaluated for AYA and pediatric testicular cancer, family history and cryptorchidism are among the few well-established risk factors [, , , , ]. Cryptorchidism incidence in Asia is similar to that in other countries , so it cannot explain the differing incidence patterns. The divergent rates between Asians and those of Asian descent indicate that environmental factors may play a role in the incidence of both AYA and pediatric testicular cancer. However, the difference might also be due to the composition of the Asian-American population in the United States, as rates differ widely in Asian countries.