An eight-year-old boy from Wiltshire is the 500th person to receive a bone marrow transplant from an unrelated donor at Bristol Children's Hospital.
Keane Meyers, from Lacock, took part in celebrations at the hospital with the cutting of a special cake.
Keane had his transplant in January from an unrelated US donor.
The centre has performed more transplants than any other in Europe since it started matching donors to patients.
Neither Keane's parents nor his sister were deemed to be a suitable match after testing.
Keane's mother, Kate Meyers, said: "To be able to find a 10-10 match, which is the best possible match they can get from an unrelated donor, is amazing, it really is.
"We are absolutely ecstatic, I think things moved so fast we didn't really have time to appreciate it."
Keane celebrated with Dr Cornish at Bristol Children's Hospital
The centre helping Keane is one of the largest in Europe and sees patients from overseas as well as from the UK.
Dr Jacqueline Cornish, who helped set it up, said: "In the beginning when we first started, people were very cynical and sceptical about it because we knew it was a very toxic and uncomfortable procedure.
"In the last five years or so the results have improved immeasurably."
One of Dr Cornish's patients from 16 years ago, Dr Dom Hurford, 32, now works as an anaesthetic registrar at the same hospital trust in Bristol.
When he was 16 he had a form of leukaemia. The chemotherapy he was given did not work, so he was given an unrelated donor bone marrow transplant.
He said having to spend such a lot of time in hospital while he was being treated helped him decide what he wanted to do as a career.
Dr Hurford said: "Being in the hospital and being around the doctors and nurses there, they are quite inspiring people and they make you think, if you can do this, maybe you can give something back.
The details of 13m donors are held on more than 50 registers across the world but there is still an acute shortage of donors from black and Asian communities.
Dr Hurford said his illness inspired him to go into medicine
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