Teenager cancer patients are missing out on specialist research, treatment and care, experts warn.
Certain cancers affect teenagers more than other age groups
They warn adolescents are "falling through the gap" between child and adult cancer services
Cancer Research UK say teenagers fail to get the emotional support they need during their illness.
The charity is calling on the government to improve services and for greater efforts to be made to include teenagers in trials.
Dr Ian Gibson MP, chair of the All Party Group on Cancer, is backing the charity's calls by putting down an Early Day Motion on Tuesday.
It is estimated that six teenagers and young adults are diagnosed with cancer in the UK every day.
Each year, around the same number of 15 to 24-year-olds as children under 15 are diagnosed with cancer.
But there are just eight specialist teenage cancer units, with a ninth under construction, in the UK, compared to 22 for children.
Experts say the lack of centres means teenagers can find themselves being treated along a five-year-old, or a 70-year-old, when their needs are very different.
Teenagers are affected by certain cancers more than other age groups.
They have particularly high numbers of leukaemias and lymphomas, bone and testicular cancers.
Cancer Research UK say the same resources should be dedicated to teenage cancer care as to paediatric services.
A group was set up 30 years ago to co-ordinate research and treatment for children with cancer, and survival rates have improved significantly since.
The group maintains a national register of all children's cancers and enrols a high proportion of patients into clinical trials within specialist paediatric centres.
However, there is no national register of cancers among older adolescents and young adults.
Some teenage cancers included on both children's and adults' registers - or omitted from both.
The charity is calling for more teenagers to be included in trials which could help their treatment, and that of others in the future.
Professor Robert Souham, of Cancer Research UK, a teenager cancer specialist, said: "Our lives change greatly in adolescence and young adulthood and developing cancer at this time can cause major disruptions to education, social life, relationships and starting work.
"Treating cancers in this age group also presents a special challenge to doctors.
"For these reasons our patients need specialised care, including access to trials and social and educational support.
"At the moment, that kind of specialist care is not generally available across the UK."
The Teenage Cancer Trust specialises in setting up units which cater for teenagers' educational needs and where they can relax and listen to music, watch TV and use computers.
Simon Davies, chief executive of the trust, said: "The number of teenagers with cancer in Britain is far more than has ever been acknowledged and there is a serious lack of provision in this area.
"You would never see a child with cancer treated anywhere but a paediatric oncology unit - it is time the same courtesy was extended to teenagers and young adults.
"This is a group of people currently invisible as far as the NHS is concerned."
Public Health Minister Melanie Johnson said: "The relatively small numbers of teenagers with cancer, coupled with the very different needs of patients within the 13 to 19 age group present particular challenges to the NHS.
"That is why we have asked the National Institute for Clinical Excellence to provide guidance for improving services for children and adolescents with cancer and enable us to develop national standards for paediatric oncology.
"We are also providing £98,000 a year funding to enable more teenage cancer patients to enter trials of the latest treatments and involving teenagers in designing services which meet their specific needs."