It's on the rise, but researchers can't be sure whether it is hormones, diet or other reasons that are causing the increase in testicular cancer.

Nor can they explain why New Zealand is going against the international patterns in the ethnic and socio-economic patterns for the disease.

Testicular cancer is rare and has a high survival rate, but it is the commonest form of cancer diagnosed among young men.

Top American cyclist Lance Armstrong, All Black Aaron Cruden and Maori Television karaoke competition host Te Hamua Nikora have all been treated for the disease.

Cruden was diagnosed in 2008, and subsequently had surgery to remove a testicle, followed by chemotherapy.

He said being diagnosed with cancer was "pretty terrifying".

"You never expect to hear you have cancer at the age of 19," said Cruden, who was named an All Black last month.

"That was a big shock ... my life was just beginning. My rugby was just starting to go well."

Researchers from Otago University at Wellington have found that New Zealand's incidence of testicular cancer has risen since the early 1990s, in line with other developed countries.

But the rate for Maori men was 50 per cent higher than that for European New Zealanders - and men on low incomes had a higher rate than those on high incomes.

Those findings are contrary to patterns overseas, where white men and those on high incomes have the higher rates.

"To our knowledge this is the only example of a non-white population having higher incidence of testicular cancer than the white population living in the same country," the researchers, led by Dr Diana Sarfati, say in the International Journal of Cancer.

"The pattern of Pacific Island and Asian rates being less than European/other men is consistent with findings elsewhere."

They say the ethnic and income patterns of the disease in New Zealand are "intriguing and unusual" and may provide clues in searching for causes of testicular cancer.

Dr Sarfati said yesterday the only well-established risk factors were being aged between 15 and 44, and undescended testicles.

Some evidence had also been found of associations with early onset of puberty, high dietary intakes of fat and dairy products, and exposure to elevated levels of the hormone oestrogen during pregnancy.

165 - number of cases diagnosed in 2006.

4 - number of deaths in 2006.

95 per cent - proportion of patients alive five years after diagnosis.