Childhood cancer survival has increased in Australia by six per cent over recent decades, despite an unexplained rise in incidence rates among the very young.

About 640 children under the age of 15 are diagnosed with cancer every year, according to the latest snapshot by the Australian Paediatric Cancer Registry.

Almost half of all cases are diagnosed in children under four.

The study by the Registry, which is funded and managed by Cancer Council Queensland, shows there has been no significant change in incidence rates among kids aged five to 14 years.

But for children aged up to four years incidence rates increased, albeit slowly, at less than one per cent per year.

Experts can't explain why and say more research is needed.

"We absolutely don't know," says Cancer Council Queensland spokesperson Katie Clift.

"We need more funding to do more research into that area, specifically into kids under four."

That aside, the outlook for children diagnosed with cancer has improved in recent years, Ms Clift said.

"It's fantastic news that the mortality rate is decreasing and the survival rate is improving," she said.

Overall childhood cancer mortality rates decreased by about four per cent a year between 1998 and 2010.

Five-year survival for all childhood cancers improved from 76 per cent in 1992-2001 to 82 per cent for 2002-11.

There were significant improvements in survival rates for leukaemia, lymphoma and neuroblastoma, she said.

But one in five kids affected will still die within five years.

"That's one in five too many," she said.

CHILDHOOD CANCER IN AUSTRALIA
- Leukaemia is the most common type of cancer diagnosed
- Boys are 16 per cent more likely than girls to be diagnosed
- Indigenous children are 36 per cent less likely to be diagnosed with cancer than non-indigenous kids
- Survival was worse for children with cancer who lived in isolated areas.
(Source: Australian Paediatric Cancer Registry)