The most common form of brain cancer in adults, glioblastoma multiforme, probably is a set of diseases, rather than a single disease, U.S. researchers said on Tuesday.
The team identified four distinct subtypes of the brain tumors, each with unique molecular characteristics, a finding they say may lead to targeted therapies.
The study also found that each subtype of glioblastoma multiforme may begin from different types of cells, meaning each needs a different treatment approach, Dr. Neil Hayes of the University of North Carolina at Chapel Hill and colleagues wrote in the journal Cancer Cell.
But the findings will not affect how doctors currently treat brain tumors, they said.
Glioblastoma multiforme, or GBM, spreads quickly to other parts of the brain, making it difficult to treat. Most people with GBM die within about 14 months of diagnosis.
In recent years, three of every 100,000 Americans have been diagnosed with GBM.
Hayes's team analyzed 206 patient samples for their study as part of the Cancer Genome Atlas network, a government-funded project to map all of the DNA activity in various cancers.
The brain tumors all look alike but had differences that were not previously recognized, Hayes said in a telephone interview.
"It would be as if you'd never known the difference between a car and a pickup truck and all of a sudden you realized that they're different," he said.
After the GBM subtypes were identified, the team looked for characteristics that defined each of the four diseases. They found "a bundle of events" that was unique to each of four subtypes of the tumor.
"These are critical events in the history of the tumor's development and spread and evidence is increasing that they may relate to the initial formation of the tumors," Hayes said.
The study also found that different subtypes of the tumor responded differently to chemotherapy and radiation.
Patients with one GBM subtype treated with aggressive chemotherapy and radiation appeared to succumb at a rate approximately 50 percent slower than patients treated with less aggressive therapy, the researchers said.
This effect was seen to a lesser degree in two of the subtypes and not at all in the fourth subtype, the researchers said.
This could mean that some classes of drugs would be expected to work for some tumor subtypes and not others, the researchers wrote.
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