Obscure etiology, unusual disparity: the epidemiology of testicular cancer in New Zealand.

PURPOSE: Testicular cancer (TC) remains perplexing, both in terms of what causes the disease and why certain populations are at greater risk of developing it. In New Zealand, an unusual ethnic disparity exists, whereby the indigenous Māori population suffer the highest rates of disease. In this study, we further describe the epidemiology of TC in the New Zealand context.
METHODS: Eligible patients diagnosed with TC between 2000 and 2011 (n = 1,800) were determined from the NZ Cancer Registry and linked to mortality data. Census data were used to estimate population incidence of TC and tumor sub-type by ethnic group. Kaplan-Meier and Cox regression analyses were used to compare survival between ethnic groups.
RESULTS: Māori males aged 15-44 were 80% more likely to be diagnosed with TC compared to European/Other males [age-standardized relative risk (RR) 1.80, 95% CI 1.58-2.05]. By contrast, disease burden was comparatively low among Pacific and Asian populations. Māori had a greater incidence of both seminoma (RR 1.88, 95% CI 1.52-2.22) and non-seminoma (RR 1.67, 95% CI 1.35-2.07) germ cell tumors than the European/Other population, reducing the likelihood that our observed disparity is driven by differential propensity to one given sub-type among Māori. Māori had poorer survival outcomes [cancer-specific adjusted hazard ratio (HR) 2.29, 95% CI 1.14-4.59] than the European/Other population.
CONCLUSIONS: Understanding the drivers of New Zealand's unusual incidence disparities--particularly between Māori and Pacific--could further our understanding of the key exposures involved in TC etiology.