Abstract
Background: Incidence rates of testicular cancer (TC) have been increasing in many countries since, at least, the mid-20th century without clear explanation. Examining the varying trends across countries and time provides clues to understanding the causes of TC.
Objective: We have presented incidence data from 41 countries and evaluated incidence trends for the 35-yr period from 1978 to 2012.
Design, setting, and participants: Cancer registry data from Cancer Incidence in Five Continents (CI5) volumes V-XI, CI5plus, and the NORDCAN database were analysed.
Outcome measurements and statistical analysis: Age-standardised rates of TC overall and by histological type were calculated. A joinpoint regression model of the natural log-transformed rates was used to calculate the average annual percent change (AAPC) in incidence. Age-period-cohort modelling was used to examine the effect of birth cohort on rates.
Results and limitations: While the highest incidence of TC remains in Northern Europe, the gap is closing between higher- and lower-incidence regions. Age-period-cohort modelling found flattening of risk among recent cohorts in Denmark and the UK, a steady increase in risk in the USA (particularly for seminomas), and an increase in risk among more recent cohorts in Costa Rica, Croatia, and Slovakia.
Conclusions: The gap between low- and high-incidence countries is closing due to increases in the former and stabilisation in the latter. Understanding the causes of these and other differences in incidence rates between, and within, countries may help further our understanding of the aetiology of this cancer.
Patient summary: We examined the rates of testicular cancer in different countries over time. These rates have been increasing, although the rates in high-incidence countries seem to be slowing down, while rates in low-incidence countries are catching up. These trends might help us understand what is causing testicular cancer in general.