Cancer services for children and young people must be reformed, an NHS advisory body says.
Most children and teenagers are treated on adult or paediatric wards
The National Institute for Health and Clinical Excellence has issued guidance to standardise cancer treatment for young people in England and Wales.
It said all under 19s must be treated in wards with services specially designed for them.
Children and teenagers are often cared for in adult or paediatric wards, which campaigners say hinders their recovery.
There are currently eight specialist cancer units for children and young people - containing facilities such as computer games, pool tables and internet access, and staffed by specialist health workers - linked to NHS hospitals.
The NICE guidance does not demand that more of the units be built.
Instead, it calls for NHS trusts to provide services tailored towards the needs of adolescents.
They should also receive care from staff trained to treat children and young people, the guidance, drawn up in conjunction with the National Collaborating Centre for Cancer, said.
Nearly 2,000 children and young people are diagnosed with cancer each year - mainly leukaemias, lymphomas and brain and spinal cancers - and there has been a 50% increase in the last 30 years.
Peter Littlejohns, who led the team which compiled the guidance, said: "The distinct needs of young people with cancer have been increasingly recognised over recent years.
"Many young people do not feel comfortable within the paediatric setting, but they have unique needs that may not be addressed within adult services."
Professor Mike Richards, the government's National Cancer Director, said: "We already have some excellent services in this country, but this guidance will provide a framework for further development."
And Simon Davies, chief executive of the Teenage Cancer Trust, said the guidance represented a "monumental shift in health strategy".
"The recognition that teenagers and young adults have a right to specialist facilities finally brings health service in line with other walks of life such as education and social care.
"The fact that NICE has recommended that age-appropriate, safe and effective services are provided with the necessary training for health professionals at every stage at all levels is music to our ears."