The puzzling incidence of testicular cancer in New Zealand: what can we learn?

BACKGROUND: Testicular germ cell tumour is the most common cancer to be diagnosed among young men. In New Zealand, we have observed some puzzling trends in the epidemiology of this disease.

METHODS: We have conducted a narrative review of available evidence regarding the puzzling epidemiology of testicular germ cell tumour in New Zealand and discussed the possible drivers of these trends.

RESULTS AND DISCUSSION: Whereas testicular cancer is most commonly a disease of White men, in New Zealand it is the indigenous Māori population that suffer by far the greatest rate of disease (age-adjusted relative risk: 1.80, 95% CI 1.58-2.05). Even more curiously, the rate of testicular germ cell tumour among Māori men aged 15-44 (28/100,000) is substantially greater than for Pacific Island men (9/100,000), a rare example of divergence between these two populations in terms of the incidence of any disease (cancer or otherwise). Our observations beg the following questions: first, why are rates of testicular germ cell tumour so much higher among Māori New Zealanders compared to the already high rates observed among European/Other New Zealanders? Second, why are rates of testicular germ cell tumour so completely divergent between Māori and Pacific New Zealanders, when these two groups typically move in parallel with respect to the incidence of given diseases? Finally, what might we learn about the factors that cause testicular germ cell tumour in general by answering these questions?

CONCLUSION: This review examines the possible drivers of our observed disparity, discusses their feasibility, and highlights new work that is underway to further understand these drivers.