"If he had a normal MRI scan six months ago when they did the carotid surgery, obviously that tells you it's a quickly growing tumor," Taylor said.
However, Saper said that the symptoms that caused doctors to perform that surgery may have actually been from the tumor. It may have been too small to see on an MRI scan at the time, he said.
Doctors at Massachusetts General Hospital have not yet released information about the exact type and grade of Kennedy's tumor. However, the majority of people older than 50 have glioblastoma multiforme, a high-grade tumor with a poor prognosis, Brem said, noting that the median survival is less than one year for someone older than 60.
"It's a serious condition, but it is treatable," Paleologos said. Initial treatment involves surgery, and then a combination of chemotherapy and radiation.
If surgery is the next step for Kennedy, surgeons will remove as much of the tumor as possible, said Dr. Michael Gruber, clinical professor of neurology and neurosurgery at NYU School of Medicine and medical director of the Brain Tumor Center of New Jersey.
Even though it grows quickly, this type of tumor generally doesn't spread, Brem said. But even surgery, chemotherapy and radiation may not be enough to keep it from recurring. "For most people, it comes back," Brem said.
To ward off a recurrence, doctors may try a new treatment called recombinant chemotherapy, Gruber said. This involves radiation five times a week with a chemotherapy drug called Temodar that is taken orally.
"The new treatment has significantly improved two-year survival from 7 percent to 27 percent," Gruber said.
And there are other experimental treatments in the pipeline for brain cancer. These prospective options include cancer "vaccines," which train patients' immune systems to attack the cancerous tissue.
Taylor is optimistic as well. "Right at this moment in history, compared to five or 10 years ago, we are making pretty great strides in treating patients, particularly in their quality of life," she said.