If Ted Kennedy's cancerous lesion is a glioblastoma multiforme, the most common kind of brain tumor, it may have been caused by a virus from the herpes family.

Last year, Duane Mitchell and his colleagues at Duke University learned that cytomegalovirus is present at elevated levels in more than 90 percent of glioblstoma multiforme tumors. Armed with that knowledge, they are testing a vaccine that fights the common virus as a brain-cancer remedy.

Their patients also receive standard cancer treatments, which includes the drug temozolomide, a staple in the treatment of some gliomas, that may also enhance the effects of the vaccine.

Mitchell is testing daclizumab, an antibody that can suppress the immune system, in combination with the vaccine. When the natural defenses bounce back after being knocked down by the drug, they may more vigorously attack the cancer-causing virus.

Brain tumors are not the only type of cancer that can be caused by a virus. Most cases of cervical cancer can be prevented by taking the vaccine Gardasil, which wards off human papillomavirus.