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People aged 15 to 39 get a different mix of cancers from children or older adults: leukaemia, lymphoma, testicular and thyroid cancer, melanoma, sarcoma and brain tumours in the younger years, then breast, cervical and bowel cancer towards 40. For decades their survival improved more slowly than anyone else's: they fell between children's and adults' hospitals and joined few trials.

Brain and spinal cord tumours range from slow-growing meningiomas and low-grade gliomas to glioblastoma, the commonest malignant brain tumour in adults, and a distinct set of childhood tumours such as medulloblastoma and diffuse midline glioma. Molecular markers now define them, and treatment is surgery, radiotherapy and, for some, drugs chosen by those markers.

Cancer in children is rare and different from adult cancer: the common types are leukaemias, brain tumours, lymphomas and embryonal tumours such as neuroblastoma and Wilms tumour, most are curable in well-resourced health systems, and the great challenge is bringing the same cures to the majority of children who live where they are not available.

Metastatic cancer means the original cancer has spread to other parts of the body, most often the bones, liver, lungs or brain. It keeps the name of where it started, is treated with therapies that reach the whole body, and can increasingly be controlled for years; with limited spread it is sometimes treated with the aim of cure.

Non-Hodgkin lymphoma is not one disease but a family of about sixty cancers of B cells, T cells or NK cells, from slow-growing follicular lymphoma to aggressive diffuse large B-cell and Burkitt lymphomas. This page is the map; each subtype has its own page with its own treatment.

Some childhood cancers are so rare that no single hospital sees enough to learn from. The NCI groups them together: heart tumours, airway papillomas, cancers of the thyroid, adrenal, nose and throat, melanoma and carcinomas more typical of adults. The answer has been international registries and expert networks that pool every case, so treatment guidance exists even without trials.

Skin cancer covers the very common and rarely dangerous basal cell and squamous cell carcinomas, the less common but more serious melanoma, and rarer tumours such as Merkel cell carcinoma and Kaposi sarcoma. Almost all of it is caused by ultraviolet light and most of it is found and cured by simple surgery.