Eight-year-old Lachie Love knows there is "an egg in his head".

But neither he - nor his little brother Harry - have been explicitly told that it is a rare and incurable brain tumour.

His mother, Liesje Love, says the "really considerate, vibrant, super-going kid" has been getting more tired and irritable of late, but cancer was not on the radar for her or his dad, Andy.

Then just before Christmas, his left eye started to turn in. The optometrist referred them to the hospital. A gamut of tests, scans and a biopsy followed, and on December 27 they got the worst news.

"We were told kids with this diagnosis have on average nine months of survival time from diagnosis, and there is no treatment. [They said], 'we will do 30 sessions of radiation and there may be a trial that he's eligible for, but essentially, go home and make memories'."

Lachie's cancer, DIPG (diffuse intrinsic pontine glioma) is an extremely aggressive tumour of the brain-stem, which mainly affects children.

Radiotherapy has bought Lachie more time, but it's a gruelling and terrifying experience for the little boy, who has to be fitted with a mask, bolted to a table and left in a room by himself.

Several times he just refused.

"At one point, one of the clinicians said - and this is my paraphrasing although they were quite direct: 'This is only buying you time, he's going to die anyway, so why would you put him and you through this if he doesn't want to do it?' But we fought to keep him doing it.

"I said: 'You've just got to give me three days and I reckon I can get him there'. And we managed to get him through the whole process."

There were dreadful side effects, including swelling in his brain.

The family was told to "prepare for the worst, hope for the best" in May, when he became paralysed down one side, was unable to walk or sit up and barely able to speak or swallow.

He needed repeat surgeries to fit a shunt to drain the fluid, and gained 30kg due to the steroids, which affected his liver and meant he was not eligible for the drug trial.

Against the odds, Lachie has rallied since then, and is now able to walk down the corridor holding onto the wall, "with someone spotting him".

His dad, Andy, has given up work to be his full-time carer.

They recently did a family trip to the Gold Coast, and last week staged an epic Halloween Party with a zombie shooting alley, candyfloss machine, face-painting and a photo booth.

"We're just focused on doing fun stuff, which has cost me a fortune in Nerf guns, I feel like we need to own shares in the Nerf gun factory, because that seems to be his reward of choice and fun activity," jokes Liesje.

"So often the day will involve Nerf gun battles around the house, and me fishing Nerf gun bullets out of dinner or out of the vacuum cleaner. It's really about focusing on what he can do, rather than what he can't do."

Liesje, a clinical psychologist who has worked with cancer patients helping them adjust to diagnosis, says they have decided not to tell Lachie about his prognosis because they want him to enjoy his life as much as he could and not be frightened.

"If he asked, I would be honest - but he hasn't asked. He knows he has an egg in his head, and he seems to accept that."

About 25 children diagnosed with brain cancers per year

Survival rates for brain cancers are among the lowest of all cancers and have barely changed in 30 years.

Brain Tumour Support Trust chair Chris Tse says brain cancers can affect "anyone, of any age or ethnicity".

"It's unfortunately one of the cancers that does affect children. It's responsible for more than 40 percent of cancer deaths in children aged 0 to 14 years, which is double the number of children who die from leukaemia."

According to the Cancer Registry, there are 329 brain cancers diagnosed in children under 15 between 2008 and 2021: an average of 25 per year.

Māori children are disproportionately affected, accounting for a third of cases overall.

"If you look at the data across all ages, the figure for Māori brain cancer cases drops to 10.3 per cent and shows the overwhelming majority of cases are in Pākehā / other European ethnicity (79.5 percent)," Tse says.

"We don't know why the incidence figures for Māori children are so high but what we do know is that paediatric brain tumours are different diseases to adult brain tumours, in terms of their biology and genetic makeup.

"I have heard it described that 'paediatric brain tumours are diseases of the developing brain whereas adult brain tumours are diseases of the ageing brain'."

Auckland University Centre for Brain Research senior research fellow Thomas Park says Māori children have double the rate of one particular type of brain tumour - medulloblastoma.

"But we don't really have a grasp of why that might be the case."

He is leading a team using artificial intelligence to analyse hundreds of brain tumour samples collected from adult and child patients in the past six years to find out whether there are differences between Māori and Pasifika.

Algorithms will be used to compare each tumour's unique "fingerprint", and look for patterns that would be impossible to spot with the human eye.

The goal is to use this information to develop personalised diagnoses and treatments.

As most clinical trials on brain tumours had been done overseas, there was "very little evidence" on how the disease manifested itself in Māori and Pasifika, says Park.

"We might find something, we might not.

"But either way, we'll be able to inform the New Zealand public and brain tumour patients whether there is a difference or not and therefore treatments that are already out there will be equally effective, or whether those differences could be targeted in a more efficient way."

Meanwhile, Lachie Love has another MRI this month to check the progress of his tumour but no further treatment is available.

-Ruth Hill/RNZ.