Scientists have shown just how mind-bogglingly complex are the genetics underpinning the development of cancer.
For the second time a team from Washington University has decoded the complete DNA of a patient with a form of leukaemia.
But the suite of key genetic mutations they found were completely different from those uncovered following analysis of their first patient last year.
The latest study does reveal some potentially significant findings.
One of the new mutations found in the second patient was also found in samples taken from 15 other patients with the same disease, acute myeloid leukaemia (AML).
The same mutation is also thought to play a role in the development of a type of brain tumour called a glioma.
A second new mutation was also found in another AML patient.
By using a state-of-art gene sequencing technique, the Washington team became the first to decode the entire genome of a cancer patient last year.
Once they have the full menu of DNA from cancer cells, the researchers can compare it with DNA from healthy cells to pinpoint genetic mutations which probably play a key role in the development of the disease.
The hope is that armed with this information scientists will be able to develop new drugs to target cancer.
But lead researcher Dr Elaine Mardis said: "Only by sequencing thousands of cancer genomes are we going to find and make sense of the complex web of genetic mutations and the altered molecular pathways in this disease.
"What we find may lead us to completely restructure the way we define tumour types and subtypes."
Her colleague Dr Timothy Ley said: "Currently, we don't have great information about how patients with this particular subtype of AML will respond to treatment, so most of them are treated similarly up front.
"By defining the mutations that cause AML in different people, we hope to determine which patients need aggressive treatment, and which can be treated effectively with less intense therapies."
The patient in the latest study was a 38-year-old man who had been in remission for three years.
Analysis revealed 64 genetic mutations which were most likely to play a role in cancer development.
Of these 52 were found in long stretches of DNA that do not contain genes, but which potentially affect how and when neighbouring genes become active.
The researchers compared the results with samples from 187 other AML patients.
They found the same mutation linked to brain tumours in 15 samples, making it one of the most common mutations yet linked to AML.
None of the mutations uncovered from analysis of the first patient was subsequently found in any other AML patient.
Dr Jodie Moffat, Cancer Research UK's senior health information officer, said: "It's exciting that these detailed studies to understand the genetic basis of cancer are now possible due to advances in technology.
"The genetic factors involved in leukaemia are particularly complex, so anything new we can learn is very welcome.
"But further research will be needed before scientists can reveal which parts of the genetic puzzle can actually be used to improve the lives of cancer patients."