CHICAGO (AFP) -- An experimental vaccine designed to treat the most common and deadly brain tumor has more than doubled the survival of patients, according to results of a small clinical study.

The vaccine, produced by the U.S. firm Avant Immunotherapeutics Inc, stimulates the immune system to attack the glioblastoma multiforme (GBM) tumor.
The clinical trial involved 23 patients with large GBM tumors.
The patients treated with the vaccine lived an average of 33 months while those receiving standard treatment typically live for an average of 14 months, said Dr. John Sampson, of Duke University in North Carolina who presented the results at the annual conference of the American Society of Clincial Oncology in Chicago.
The study also showed the vaccine slowed the return of the tumor after surgery. The tumor for those treated with the vaccine reappeared in 16.6 months compared to the usual six months.
The GBM is an aggressive cancer with a poor prognosis, brain specialist Mark Gilbert of the M.D. Anderson Cancer Center in Texas told reporters.
The tumor kills 50 percent of patients during the first year after diagnosis and few live beyond three years. Without treatment the tumor grows back between two to three months after being surgically removed.
The GBM tumor is the same that afflicts longtime U.S. Senator Edward Kennedy.
The experimental vaccine, administered with chemotherapy to stimulate an immune response, is aimed at proteins linked to tumor cells.
A much larger clinical trial was planned for later this year, Gilbert said.
About 22,000 cases of malignant tumors of the brain and bone marrow will be diagnosed in 2008 in the United States and 13,000 people will die, according to the American Cancer Society.