WEDNESDAY, Sept. 4 (HealthDay News) -- A drug used against a common virus may lengthen the lives of people with a deadly form of brain cancer, a preliminary study suggests.

Writing in the Sept. 5 issue of the New England Journal of Medicine, researchers reported on 50 patients who were given the antiviral drug valganciclovir (Valcyte) to help treat glioblastoma. The cancer is the most common form of brain tumor in adults, and it carries a dismal prognosis -- with a typical survival of just over a year.

These 50 patients, however, fared far better, researchers found.

After two years, 62 percent were still alive. Of the 25 who took the antiviral continuously, 90 percent were still alive. That compared with just 18 percent of patients who received most of the same treatments -- including surgery and chemotherapy -- but did not take Valcyte.

"These data are by far the best ever seen for these patients," said lead researcher Dr. Cecilia Soderberg-Naucler, of the Karolinska Institute in Stockholm, Sweden.

A brain cancer expert not involved in the research also voiced enthusiasm. "These are very exciting data," said Dr. David Reardon, director of neuro-oncology at the Dana-Farber Cancer Institute in Boston.

But he also urged caution because there are many unknowns, and the findings need to be verified in a controlled clinical trial -- in which patients would be randomly assigned to take Valcyte or not, and then followed over time.

Valcyte is a pill used to treat cytomegalovirus (CMV) eye infections in people with AIDS. CMV is a very common virus -- up to 80 percent of adults contract it by age 40 -- and it usually causes no harm in someone with a healthy immune system.

Researchers have found, however, that CMV dwells in the tumor cells of most people with glioblastoma, which suggests that the virus contributes to the cancer in some way.

One recent lab study found that when certain cancer-promoting gene mutations are present, CMV might speed the growth of glioblastoma.

"It appears that the virus alone is not sufficient to cause any human tumors," said Chang-Hyuk Kwon, one of the researchers on that study.