A grim diagnosis: Kennedy's brain cancer is worst kind

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.