Dangerous brain tumors hijack the brain’s existing blood supply throughout their progression, according to new research. The tumors grow only within narrow potential spaces between and along the brain’s thousands of small blood vessels.

These findings contradict the concept that brain tumors need to grow their own blood vessels to keep themselves growing, and they help explain why drugs that aim to stop growth of the new blood vessels have failed in clinical trials to extend the lives of patients with the worst brain tumors.

In fact, trying to block the growth of new blood vessels in the brain actually spurs malignant tumors called gliomas to grow faster and further, the research found. On the hopeful side, the research suggests a new avenue for finding better drugs.

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The discoveries come from a University of Michigan Medical School team in Ann Arbor studying tumors in rodents and humans, and advanced computer models, in collaboration with colleagues from Arizona State University in Tempe. The work was published in Neoplasia (2014; doi:10.1016/j.neo.2014.06.003).

The vessels that the researchers studied feed the brain’s constant need for energy and communication with the rest of the body. They have a special vessel wall structure that protects the brain from infection or other blood-borne dangers.

The new findings show that tumor cells grow exclusively within the spaces around the vessels, close enough to draw their own energy and fuel their growth in the same way normal brain tissue does. Instead of spawning their own offshoots of these vessels as the tumor cells divide, they simply crowd out the normal cells in the immediate area and continue to fill the spaces between neighboring vessels.

This continued autovascular growth, as the researchers called it, was detected from the very beginning to the final stages of tumor progression. It runs directly counter to the theory of neoangiogenesis that has driven the use of certain drugs to treat brain tumors such as glioblastoma multiforme and other cancers.

Last year, two clinical trials showed that glioblastoma patients taking an anti-angiogenic drug as part of treatment did not survive any longer, and in some cases suffered more side effects than patients who did not get the drug. Patients whose glioblastoma returned after treatment also used the drug to reduce swelling.

The researchers caution that it is far too soon for patients to make medical decisions based on their findings. But they note that further research on how new therapies will directly affect the tumor cells growing along blood vessels is already under way.