They're the biggest cancer killer of children and adults under 40, yet brain tumours currently receive just 1% of the national spend on cancer research.

The charity Brain Tumour Research (BTR) would like to see this change, and is calling for a bigger piece of the cancer research pie, so that adults and children - like five-year-old Ashya King, whose parents recently sparked a police hunt after taking him abroad for brain tumour treatment - have more, and better, treatment options in the UK.

There have been huge improvements in survival rates for leukaemia, breast, bowel and prostate cancers in recent years, and higher spends on research for these forms of the disease have played a big part in this, BTR points out (t ogether, these cancers receive 55% of the national research spend).

Meanwhile, the number people diagnosed with brain tumours - and the number of people dying from them - is on the rise. In 2012, brain cancer incidence was 23% higher for men and 25% higher for women than in 1970, and brain cancer deaths rose 10% for women and 15% for men between 1970 and 2011.

Only 18.8% of brain tumour patients survive beyond five years, compared with an average of 50% across all cancers.

Sue Farrington Smith, BTR's chief executive, stresses that a chronic lack of funding has made brain tumours the "poor cousin" of cancer research.

"The recent heartbreaking story about Ashya King and the difficulties the family faced have meant that brain tumours have been talked about more now than they have been for years, and it's in the public consciousness," she says. "We need people to know that more and better funding into brain tumours could bring about better outcomes."

THE NUMBERS

Around 16,000 people are diagnosed with a brain tumour every year in the UK - high profile examples include singer Russell Watson and actor Martin Kemp. American singer Sheryl Crow also had a brain tumour, and also survived.

There are around 130 different types of brain tumour. Only a round half are cancerous, while the rest are benign - although these can still be life-threatening, because of the damage they can do to the brain.

It's not known what causes brain tumours, and while possible risk factors, such as mobile phones, have been investigated, no strong evidence has been found, notes Cancer Research UK. However, not enough is known about the possible link between mobiles and brain tumours to completely rule out a risk.

Primary brain tumours, which arise from the brain, are very rare, and secondary tumours which have spread to the brain from cancers in other parts of the body, are more common - BTR says up to 40% of all cancers eventually spread to the brain.

SPOTTING THE SIGNS

Brain tumours can be difficult to detect and symptoms can vary widely, depending on where in the brain they are, but Dr Kevin O'Neill, a consultant neurosurgeon at Imperial College Healthcare NHS Trust in London, says the most common signs are headaches and seizures.

"But of course, headaches and seizures are reasonably common, and most people with headaches don't have a brain tumour," he stresses. "The worrying pattern of headaches is typically worse in the morning, perhaps waking you from sleep, and getting worse over time. What's key is that they're often different from your 'usual' headache - most people have had enough headaches to know what theirs feels like."

Headaches related to brain tumours are usually linked to increasing mass and pressure from the tumour, and are often worse in positions like lying down, where gravity adds to the problem.

Raised pressure can also lead to nausea and vomiting or progressive neurological problems as the tumour affects the surrounding brain. These may include clumsiness, visual disturbance or weakness on one side of the body, often similar to stroke symptoms.

Other signs may include changes in senses, including an impaired sense of smell and hearing, problems with speech, writing or drawing, and difficulty with averting the eyes upwards.

WHAT ABOUT PROTON THERAPY?

According to Dr O'Neill, the prognosis for brain tumours is extremely variable, as some may be very slow growing and never cause a problem, while others are very aggressive and have a poor prognosis even with maximum treatment, which includes neurosurgery, radiotherapy and chemotherapy.

Proton therapy, the treatment Ashya King was taken overseas to receive (he's currently undergoing treatment in a Czech clinic), will not be available for the treatment of brain tumours in the UK until 2018.

However, Dr Matt Williams, a consultant clinical oncologist at Imperial College NHS Trust, says that while there are some rare tumours where proton therapy may be beneficial, for the most common types of tumour, it doesn't appear to be advantageous.

"Proton therapy is just another type of radiotherapy, and carries many of the same benefits and risks. Those where it offers an advantage are the tumours where we know we want to give a big dose, but where we're limited by a delicate structure next to the tumour. Those where it isn't as useful are where the tumour is mixed in with the normal tissue, so we'd find it harder to give a higher dose," he explains.

"The other issue is that the gap between what you can achieve with conventional radiotherapy and proton therapy has narrowed over the last few years, as the technology for conventional radiotherapy has improved."

UNIQUE CHALLENGES

BTR are determined to see more funding ploughed into brain tumour research. However, the challenges are not straightforward.

"Brain tumours are rare," Dr Williams notes. "For some tumour types, the survival rate is poor, so there isn't a large army of survivors to push for more research. There are some very dedicated patients and families of patients who've died who spend a lot of time trying to raise awareness, but there just aren't the numbers."

Poor survival rates for some types of brain tumour also arise because the brain is very delicate, and is protected by the 'blood-brain barrier', adds Dr Williams.

"Because of this, drugs that work on brain tumour cells in the lab often don't work in humans," he explains. "It's a difficult tumour to work on - getting hold of the tumour cells is hard - we have to open your head."

Mapping how a tumour changes over time is difficult, he says, as few patients have repeated operations, and because brain tumours appear to be different to other tumours, what's been learned from other cancers can't always be directly applied.

Dr O'Neill says that while neurosurgery is very important for the treatment of brain tumours, there's very little funding for surgical research, and the surgery is very complex.

"Beating brain cancer will require a critical mass of funding to attract talented individuals into the field, who would otherwise work in areas better resourced. Without such a critical mass we cannot produce high quality research."

:: For more information about brain tumours, visit www.braintumourresearch.org