A malignant glioma _ the diagnosis doctors gave Sen. Edward M. Kennedy _ is the worst kind of brain cancer.

Malignant gliomas strike almost 9,000 Americans a year. Survival statistics are grim _ few live three years and for the worst subtype, half die within a year.

Who lasts longer _ and some do _ depends on exactly what form of glioma someone has, whether surgeons can cut most of it out, age and some other medical details.

Kennedy's doctors didn't mention surgery, suggesting that may not be a possibility for him.

"As a general rule, at 76, without the ability to do a surgical resection, as kind of a ballpark figure you're probably looking at a survival of less than a year," said Dr. Keith Black, chairman of neurosurgery at Cedars-Sinai Medical Center.

On the plus side, scientists are studying new approaches _ adding a drug called Avastin to standard treatment, or even brewing up customized vaccines to help the body fight back. While they're still experimental, many glioma experts advise newly diagnosed patients to seek out specialized cancer centers and ask if they're a good candidate for a research study up front.

"Considering how poorly they do despite standard treatment, it is always best to seek a clinical trial," said Dr. Deepa Subramaniam, director of the brain tumor center at Georgetown University's Lombardi Comprehensive Cancer Center. "They are not likely to do worse."

Kennedy was hospitalized Saturday after a seizure. Tuesday, doctors at Massachusetts General Hospital announced the reason, a malignant glioma in his left parietal lobe, a brain region that governs sensation but also plays some role in movement and language. Doctors were awaiting further tests before choosing treatment, but they cited radiation and chemotherapy as the usual approach.

Kennedy's age and the mention of upfront chemotherapy mean the glioma is almost certainly one of the two worst forms: a glioblastoma _ the fastest-killing brain tumor, known for claiming entertainer Ethel Merman and Republican political strategist Lee Atwater _ or the only somewhat less aggressive anaplastic astrocytoma, Subramaniam said.

Malignant glioma "usually is a synonym for a glioblastoma," agreed Dr. Robert Laureno, neurology chairman at Washington Hospital Center in the nation's capital.

The American Cancer Society puts the five-year survival rate for patients over age 45 at 16 percent for those with anaplastic astrocytomas, and 2 percent or less for those with glioblastomas.

Patients fare best when surgeons can cut out all the visible tumor, Black said. That isn't a cure _ doctors know they're leaving cancerous cells they just can't see.

But about 40 percent of the time, surgery isn't an option. The cancer, which digs tentacle-like roots into normal brain tissue, may be too deep or located so closely to critical brain regions.

Moreover, "it doesn't help to take 50 percent or 60 percent of the tumor out," Black said.

Standard treatment is about six weeks of fairly high-dose radiation along with a chemotherapy pill named Temodar, and then additional Temodar for at least six months or until the tumor stops responding.

The older the patient, the worse the prognosis. But some people fare much better _ especially those with a subtype where another glioma form, called oligodendroglioma, is mixed with the primary tumor, Black said. They generally survive three times as long as people with pure glioblastomas.

The tumor's size _ which also wasn't revealed _ is key, too, added Dr. Lynne Taylor of Seattle's Virginia Mason Cancer Center and the American Academy of Neurology. An 8-centimeter tumor is pretty big for chemo and radiation to blunt, while a 1cm tumor is easier.

Also, the fairly recent addition of Temodar has brought a slight increase in the number of patients who beat average survival odds, she added.

"You're fighting an uphill battle," is what Taylor tells her patients _ and then immediately urges them to live as if they'll be one of the lucky ones.

Whatever the statistics, the news is grim. And what symptoms will appear first depends on exactly where in the parietal lobe the tumor sits and "how that individual's brain is wired," Laureno said.

Among the possibilities: Loss of sensation on the right side of the body, problems with movement in the right arm and leg, eventual problems speaking or even vision problems in the right eye.

There are some experimental therapies that researchers are watching closely, including:

_Adding the colon cancer drug Avastin to standard treatment. Avastin chokes off tumors' blood supply, and initial studies suggest it can help shrink gliomas. Whether that helps survival isn't yet known, but Black says even though this use is experimental, more and more specialists are prescribing it right after diagnosis.

_Trying experimental cancer vaccines. Brain tumors often can't be seen by the immune system. So scientists take cells from the surgically removed glioma, put them on the immune cells and give them back to the patient. Small studies at Cedars-Sinai suggest the approach improved two-year survival from 8 percent of glioblastoma patients to 42 percent, Black said. But it's only an option for surgery candidates.