TUESDAY, May 20 (HealthDay News) -- Massachusetts Sen. Edward M. Kennedy, the last surviving brother in an American political dynasty, has a malignant brain tumor, his doctors reported Tuesday.

Doctors treating the 76-year-old senator, who has been in Massachusetts General Hospital in Boston since he suffered a seizure on Saturday, said that tests showed a tumor in his left parietal lobe. They said preliminary results from a biopsy of the brain identified the cause of the seizure as a malignant glioma, the Associated Press reported.

Dr. Lee Schwamm, vice chairman in the department of neurology, and Dr. Larry Ronan, a primary care physician, issued the following statement, according to MSNBC: "Over the course of the last several days, we've done a series of tests on Senator Kennedy to determine the cause of his seizure. He has had no further seizures, remains in good overall condition, and is up and walking around the hospital. Some of the tests we had performed were inconclusive, particularly in light of the fact that the senator had severe narrowing of the left carotid artery and underwent surgery just six months ago."

They added: "However, preliminary results from a biopsy of the brain identified the cause of the seizure as a malignant glioma in the left parietal lobe. The usual course of treatment includes combinations of various forms of radiation and chemotherapy. Decisions regarding the best course of treatment for Sen. Kennedy will be determined after further testing and analysis. Sen. Kennedy will remain at Massachusetts General Hospital for the next couple of days according to routine protocol. He remains in good spirits and full of energy."

The American Cancer Society estimates that 21,810 malignant tumors of the brain or spinal cord will be diagnosed this year in the United States. Approximately 13,070 people -- 7,420 men and 5,650 women -- will die from these malignant tumors. The cancers account for about 1.3 percent of all cancers and 2.2 percent of all cancer-related deaths in the United States.

A patient's prognosis depends on the "grade" of the tumor, said Dr. Isabelle Germano, co-director of The Radiosurgery Program at Mount Sinai Medical Center in New York City. Five-year survival rates for low-grade (grade 1) tumors can be as high as 95 percent; for grade 4 tumors, five-year survival plummets to about 5 percent, she said.

Dr. Deepa Subramaniam, director of the brain tumor center at Georgetown University's Lombardi Cancer Center in Washington, D.C., said younger people tend to be diagnosed with low-grade tumors while older individuals tend to have more aggressive ones.

The first evidence that a person has a malignant tumor is often a seizure like the one Kennedy suffered, or stroke-like symptoms.

"One of the most important things is whether this tumor is in a location that would allow him [Kennedy] to have surgery, because that will definitely improve the chances of long-term success," Subramaniam said. Only about 40 percent of tumors are operable, she added.

The parietal lobe, where Kennedy's tumor appears to be located, governs strength in one-half of the body. "It would leave him with weakness in one half of his body, so they might not take it out," Subramaniam said.

Without surgery, patients are left with chemotherapy (only one drug is currently approved for malignant glioma) and radiation, often given concurrently for the first six weeks. If that is well tolerated and if the tumor hasn't grown, patients might receive additional chemotherapy for the next five months or longer, Subramaniam said.

In the most aggressive form of the cancer -- grade 4 -- patients can live for about a year with the full complement of therapies, Subramaniam said. Without treatment, however, the prognosis is usually a few months.

But the outlook isn't always that grim. Subramaniam said she has examples of patients who have lived for two years, "so it's not clear why some patients live so long while others die within a year."

Dr. Jonathan Friedman, director of the Texas Brain and Spine Institute in College Station, said that, given a "diagnosis of malignant glioma, surgery is generally not curative. The primary role of surgery is to biopsy and ascertain the diagnosis and, in some circumstances, there's a role for debulking or removal of a significant volume of tumor. But in some circumstances that's not possible or not desirable.

"But malignant glioma are infiltrative tumors," added Friedman, who's also an assistant professor of surgery and neuroscience and experimental therapeutics at the Texas A&M Health Science Center College of Medicine. "They don't have good margins. They grow into the brain, which makes sense because they are made out of brain cells. Because of that, they generally cannot be removed in their entirety."

Added Dr. Keith L. Black, chairman of the department of neurosurgery at Cedars-Sinai Medical Center in Los Angeles, "Age will be a very strong predictor of how well the senator does, it's probably a stronger predictor than the grade of the tumor. And the fact that the senator is 76 will be a challenge to overcome in his overall prognosis. We also know that surgery is beneficial if it can be safely done and the fact that in the news release doctors at Mass General are not talking about doing surgery early on may mean that he's not a candidate for surgery and that may be because the tumor is too close to language areas or motor areas. And if one is not able to remove all of the tumor that one can see on the MRI scan that is not a positive for overall prognosis."

Kennedy, the second-longest serving Democratic senator currently in Congress, suffered a seizure while at his family's Hyannisport compound and was taken by helicopter to Boston Saturday morning.

In October 2007, a partially blocked carotid artery in Kennedy's neck was discovered during a routine magnetic resonance imaging (MRI) examination. Doctors cleared the blockage, and Kennedy was released to convalesce in Hyannisport.

Dr. Otis W. Brawley, chief medical officer for the American Cancer Society, called Kennedy an "unparalleled leader in the fight against cancer and for access to quality health care for all Americans throughout his distinguished career in the United States Senate. He yields to no one in his accomplishments and in his efforts to bring all the resources of the nation to bear in fighting cancer and other diseases, to reigning in the tobacco industry, and to extending health insurance coverage to all Americans, especially the most vulnerable among us."

"As with anyone who has been diagnosed with brain cancer or who has had a family member diagnosed with this disease, we wish the Senator well, and hope that his treatment is effective and that he is able to continue the legacy for which he is so well known," Brawley added.

Kennedy is the youngest of nine children, and became a U.S. senator in 1962. His older brother, President John F. Kennedy, was assassinated in 1963. Another brother, Robert Kennedy, who was also a U.S. Senator, was assassinated in 1968 during his presidential campaign.

More information

The National Library of Medicine has more on glioma.

SOURCES: Deepa Subramaniam, M.D., director, brain tumor center, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, D.C.; Isabelle M. Germano, M.D., professor of neurosurgery, and director, The Radiosurgery Program, Mount Sinai Medical Center, New York City; Jonathan Friedman, M.D., assistant professor of surgery and neuroscience and experimental therapeutics, Texas A&M Health Science Center College of Medicine, and director, Texas Brain and Spine Institute, College Station; Associated Press; Keith L. Black, M.D. chairman, department of neurosurgery, Cedars-Sinai Medical Center, Los Angeles; American Cancer Society, news release, May 20, 2008; MSNBC; Associated Press

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