Doctors can treat many brain tumours more effectively by first ascertaining their genetic characteristics, rather than relying on the standard practice of studying tissue samples under a microscope, two teams of researchers reported last week.
The findings could alter diagnosis and treatment decisions for thousands of patients, experts said.
It may boost the case for "precision medicine", in which cancer treatment is customised according to the genetic make-up of the tumour.
"Prognosis is going to be more accurately delineated by these kinds of genetic sub-types, outstripping the value of looking through a microscope," said Dr David J. Langer, the chief of neurosurgery at Lenox Hill Hospital in New York, United States, who was not involved in the research.
Doctors treating other types of cancer, particularly breast cancer, have already established genetic sub-types to help guide treatment.
The two new papers are a large step in bringing the same approach to brain cancer treatment, said Dr Langer.
About 23,000 Americans develop a brain tumour each year and about 14,000 die of one each year.
The two reports, published in The New England Journal Of Medicine, focused on gliomas, which account for roughly a third of brain cancer cases.
Some gliomas become aggressive, like the cancer that recently killed Mr Beau Biden, son of US Vice-President Joe Biden. But doctors have not had a rigorous way of identifying which tumours will become deadlier before they do so.
In the new studies - one coordinated by the National Institutes of Health, the other led by the Mayo Clinic and the University of California, San Francisco - research teams performed multiple genetic analyses on 1,380 tumours.
Both teams found that the tumours could be grouped into a few categories which, in turn, could be determined by looking at a handful of genetic glitches.
Tumours with one genetic profile, for instance, were relatively slow growers and responsive to drug treatment, making them good candidates for chemotherapy alone, rather than combined with radiation.
Tumours in another category grew relatively slowly, but were not as responsive to drugs, so combined therapy might be the best option.
And those in a third category were nascent aggressors, for which the prognosis is usually dim. But catching those tumours early will, at least, give families time to enrol in experimental trials, the researchers said. This will also give patients and their families more specific guidance on which treatments and trials may be most suitable.
Genotyping will make research trials more focused, said Dr Daniel J. Brat, vice-chairman of pathology and laboratory medicine at Emory University and lead author of one of the new studies.
Currently, doctors examine cancerous tissue and rate it according to stages and grades. A doctor's judgment varies "depending on where you were trained, when, and by whom," said Dr Brat.
By relying more extensively on genetic profiles, "all that variability will go away", he said.
Previous research had identified these genetic markers as important.
Many brain surgeons have used genotyping along with standard biopsy ratings to guide treatment. But the new papers conclude that the genetic markers should be central in one's diagnosis and prognosis, rather than complementary.
The New York Times