Health reporter, BBC News
Young people with cancer tend to do better if they are in clinical trials
Teenagers with cancer are not being included in UK clinical trials which could improve their chances of survival, according to researchers.
Trials from 2005 to 2007 recruited only 25% of 15 to 19 year olds, compared with 43% of those aged 10 to 14, the British Journal of Cancer reported.
No-one aged over 16 was included in a brain cancer trial despite four trials being available, the researchers said.
Experts said the age range of trials often excluded teenagers.
Study leader Dr Lorna Fern, who co-ordinates research into teenagers and young adults with cancer at the National Cancer Research Institute in London said the US and Australia had also reported a similar trend.
In this first UK study of patients up to the age of 24 who had leukaemia, lymphoma, cancers of the brain and the central nervous system, bone sarcomas and male germ cell tumours, there was a dramatic decline in trial entry after the age of 15.
By the age of 20-24, recruitment to trials was only 13%.
In the second year of the study, recruitment to trials had increased slightly but still fell massively after the age of 15 from 51% to 19%.
Inclusion in trials has been shown to improve cancer survival because it provides access to new drugs, better quality of care through frequent monitoring and access to a wider group of specialists.
"In 2005 NICE issued guidance that said all children and young people should be offered entry into a clinical trial," Dr Fern said.
One problem for the poor recruitment of teenagers to trials is that they fall between children and adult specialities, she explained.
"A lot of adult trials have an age eligibility of 18 so, if you're 16 with a carcinoma you won't be eligible," she added.
The National Cancer Research Institute and the Children's Cancer and Leukaemia Group have plans in place to improve the situation on the basis of the figures, Dr Fern said.
Simon Davies, chief executive of Teenage Cancer Trust and one of the authors of the study, said they wanted to see the number of teenagers and young adults in clinical trials double over the next five years.
"Young people are constantly falling through the gap between paediatric and adult cancer specialists and there are not enough trials for the types of cancers that affect them.
"For the ones that do exist, often the age range excludes them from being treated.
"In too many cases they are simply not offered the choice of entering a trial."
He added that clinicians are already working to close the gap between child and adult trials so that young people can qualify.
Kate Law, Cancer Research UK's director of clinical trials, said the research would be used as a baseline against which to measure progress.
The charity has announced a £1.5bn research strategy over the next five years to improve survival from cancer.
"Highlighting poor recruitment of young people onto clinical trials and introducing measures to improve this will be a vital contribution to reaching our goal."