A "revolutionary" new class of cancer drug that can treat a wide range of tumours has been approved for use in Europe for the first time.
Tumour-agnostic drugs do not care where the cancer is growing in the body as long as it has a specific genetic abnormality inside.
UK doctors testing the drugs said they were "a really exciting thing".
They said the approach had the potential to cure more patients and cut side-effects.
The drug that has been approved is called larotrectinib.
Charlotte Stevenson, a two-year-old from Belfast, was one of the first patients to benefit.
She was diagnosed with infantile fibrosarcoma, a cancer of the body's connective tissue.
She has been treated with larotrectinib as part of a clinical trial at the Royal Marsden Sutton, in London, for the past year.
Her mum, Esther, said: "We knew that our options were limited [so] we decided to give it a try and are so glad that we did.
"We have been able to watch Charlotte develop and grow at a rapid rate, making up for lost time in so many ways and amazing us all with her energy and enthusiasm for life.
"She can now have a relatively normal life and, best of all, the drug has had an incredible impact on the tumour."
Charlotte's tumour was caused by a genetic abnormality known as an NTRK gene fusion.
One part of her DNA accidentally merged with another and the alteration in the blueprint for her body led to the growth of her cancer.
But NTRK gene fusions are not unique to sarcomas - they also appear in some brain, kidney, thyroid and other cancers.
"It is a really exciting thing, as is it works across a range of cancers. It's not confined to one," Dr Julia Chisholm, a children's cancer consultant at the Royal Marsden Hospital.
NTRK mutations are relatively rare, but other targeted therapies are in development.