Nov 20 (Reuters) - New data from a midstage trial show that Celldex Therapeutics Inc's experimental brain cancer vaccine, combined with standard therapy, continues to improve chances of survival for patients with recurrent cancer.

The vaccine, designed to enlist the body's immune system to fight glioblastoma multiforme (GBM), showed that 25 percent of patients given Celldex's Rintega along with Roche Holding AG's Avastin were alive after two years, compared with no survivors in the group of patients given only Avastin.

Results from the 73-patient trial were presented on Friday at the Annual Scientific Meeting of the Society for Neuro-Oncology.

"The long-term survival benefit observed in this study is unprecedented," Dr. David Reardon, clinical director at Dana-Farber Cancer Institute's Center for Neuro-Oncology, and the study's lead investigator said in a statement.

Rintega, which was granted breakthrough therapy designation by the U.S. Food and Drug Administration last year, targets a specific genetic mutation that occurs in about 30 percent of GBM tumors.

Currently, the median survival for such patients with recurrent GBM is about nine months, Celldex said.

The latest trial results showed that 32 percent of patients treated with Rintega, also known as rindopepimut, and Avastin, or bevacizumab, were alive after 18 months, compared with 13 percent of those given only Avastin.

Celldex has previously reported that the trial met its main goal of showing that Rintega patients were more likely to be alive after six months without their cancer worsening.

Celldex said it expects to report early next year interim results from a study of Rintega in patients with newly diagnosed GBM.

(Reporting by Deena Beasley; Editing by Jonathan Oatis)