Sen. Ted Kennedy has been diagnosed with a malignant brain tumor, doctors at Massachusetts General Hospital announced Tuesday, four days after the Democratic senator was rushed to the hospital following seizures.
Kennedy, 76, was diagnosed with the tumor Tuesday morning after he underwent a biopsy.
"Preliminary results from a biopsy of the brain identified the cause of the seizure as a malignant glioma in the left parietal lobe," his doctors said in a statement, adding that treatment would likely include "combinations of various forms of radiation and chemotherapy."
The senator has been hospitalized in Boston since Saturday, when he was airlifted from Cape Cod after a seizure at his home. He suffered another one en route to the hospital, sources told FOX News.
His wife and children have been with him each day.
In an e-mail sent to friends, Kennedy's wife, Vicki, acknowledged the family had been "pitched a real curveball," but said "this is only the first inning." She said the family was consulting with experts and seeking multiple opinions.
"Teddy is leading us all, as usual, with his calm approach to getting the best information possible. He's also making me crazy (and making me laugh) by pushing to race in the Figawi this weekend," she said, referring to the annual sailing race from Cape Cod to Nantucket.
His doctors said that he was in "good condition" and had not suffered any more seizures since Saturday.
Kennedy's colleagues on Capitol Hill reacted with shock and sadness Tuesday morning, but expressed confidence in his ability to fight through the illness.
"Every one of us knows what a big heart this fella has. He's helped millions and millions of people," said fellow Massachusetts Democratic Sen. John Kerry. "Everybody needs to pull for him and his family and remember that this guy is an unbelievable fighter."
"I'm betting on Senator Kennedy," said Sen. Arlen Specter, R-Pa., who himself has been battling Hodgkins lymphoma. "He's been such a champion on so many causes ... he's been a shining example of crossing the aisle."
In 1993, Spector was diagnosed with an inoperable brain tumor, and after getting a second opinion, had it removed and inspected and determined not to be malignant. He told FOX News maybe Kennedy's diagnosis is wrong, adding that will power is the key to beating cancer.
"I can tell you from my own experience that will power is very important — stay on the job, keep up regular duties, play squash," said Spector. "If tenacity can do it, Kennedy will be a survivor."
According to sources familiar with the situation, the prognosis for Kennedy is not optimistic and word is circulating through political circles in Massachusetts and on Capitol Hill that because the tumor is inoperable it can only be dealt with through chemotherapy and radiation.
Malignant gliomas are a type of brain cancer diagnosed in about 9,000 Americans a year — and the most common type among adults. It's an initial diagnosis: How well patients fare depends on what specific tumor type is determined by further testing.
Average survival can range from less than a year for very advanced and aggressive types — such as glioblastomas — or to about five years for different types that are slower growing.
"The news has been met throughout the country with great concern," said House Speaker Nancy Pelosi, D-Calif.
If Kennedy were to resign or die in office, state law requires a special election for the seat no sooner than 145 days and no later than 160 days after the vacancy occurs. He was re-elected in 2006 and is not up for election again until 2012.
Dr. Lee Shwamm, vice chairman of the Department of Neurology at Massachusetts General, and Dr. Larry Ronan, Kennedy's primary care physician, said in their statement that Kennedy will continue to undergo testing to determine the best course of treatment.
"Senator 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," they said.
Sen. Robert Byrd, D-W.Va., the longest-serving member of the Senate, wept as he prayed for "my dear, dear friend, dear friend, Ted Kennedy" during a speech on the Senate floor.
"Keep Ted here for us and for America," said the 90-year-old Byrd, who is in a wheelchair. He added: "Ted, Ted, Ted. My dear friend. I love you and miss you."
President Bush released a statement saying "Laura and I are concerned to learn of our friend Senator Kennedy's diagnosis.
"Ted Kennedy is a man of tremendous courage, remarkable strength, and powerful spirit. Our thoughts are with Senator Kennedy and his family during this difficult period. We join our fellow Americans in praying for his full recovery."
Kennedy, the second-longest serving member of the Senate and a dominant figure in national Democratic Party politics, was elected in 1962, taking over for family friend Benjamin A. Smith ll, who served as a placeholder in the seat originally won by Kennedy's brother, John F. Kennedy. John Kennedy went on to become president and Ted Kennedy ran for his seat when he turned 30 and was constitutionally eligible to enter the Senate.
The Kennedy's eldest brother, Joseph, was killed in a World War II airplane crash. President Kennedy was assassinated in 1963 and his brother Robert was assassinated in 1968.
Kennedy is active for his age, maintaining an aggressive schedule on Capitol Hill and across Massachusetts. He has made several campaign appearances for Sen. Barack Obama in February, and most recently last month.
FOX News' Major Garrett, Chad Pergram and Trish Turner and The Associated Press contributed to this report.