A genetic study revealing an aggressive blood cancer to be at least 11 different diseases could pave the way to potentially life-saving personalised treatments.
Scientists analysed 111 genes known to be linked to acute myeloid leukaemia (AML) in blood and bone marrow samples taken from 1,540 patients.
They uncovered 5,234 "driver" mutations - altered regions of DNA that affected the prognosis of patients and could be used to characterise distinct "strains" of the disease.
Patients were divided into 11 groups, each with its own "constellation" of genetic changes and set of clinical features.
Nearly all (97%) had at least one mutation and 86% had two or more, and their genetic make-up strongly predicted the way they responded to chemotherapy.
The study, the deepest investigation of a cancer's genetic background conducted to date, is expected to change the way AML is diagnosed and treated.
In future, new patients could be given blood tests that show which of them are likely to respond well to standard therapy and who has drawn the short genetic straw and may need more intensive or experimental treatments.
British scientists from the Wellcome Trust Sanger Institute in Hinxton, Cambridgeshire, who took part in the international study, are now conducting a similar analysis of tumour samples from 1,000 breast cancer patients.
Results from that research are expected before the end of the year.
AML, which develops in the bone marrow, is a fast-growing and aggressive cancer that often requires months of intense chemotherapy. In 2013, there were around 2,900 new cases of the disease in the UK.
Professor Peter Campbell, who led the Sanger Institute team, said: "The genetic changes we see fundamentally cause leukaemia. They dictate the way leukaemia cells will behave; they dictate why that cell is a leukaemia cell.
"What we see in this study is that there's a huge complexity, there's a huge variability across different patients. No one patient's leukaemia is like any other patient's leukaemia. It's that complexity that drives the variation we see in the clinic.
"You can take two patients who have what look like the same leukaemia under the microscope and apply treatment with exactly the same therapy, and one patient will be cured and one will relapse and die very quickly.
"What we can see in this dataset is that clinical variability is strongly predicted by the underlying genetics.
"The take home message I think is strongest from this study is that ... a large proportion of what will happen to a patient is written and encoded in the genetic changes that (a) cancer has."
Currently only a few diagnostic laboratories in the UK, including two in Oxford and York, are equipped to carry out the tests.
But Prof Campbell expected them to become routine in the near future, as genetic testing is increasingly brought into NHS clinics.
Genomics England, wholly owned by the Department of Health, is engaged in a project to sequence 100,000 genomes - complete genetic codes - of NHS patients and their relatives.
The research, published in the New England Journal of Medicine, was only made possible by the accelerating rate at which scientists are turning up genes linked to cancer.
"In this study about half the genetic changes were in genes we didn't know about five years ago," said Prof Campbell.
Four years ago scientists announced that breast cancer could be classified as 10 broadly different diseases according to its genetic features.
British and Canadian researchers came to the conclusion after analysing 2,000 tissue samples taken from the tumours of women with breast cancer.