BOSTON, Massachusetts (CNN) -- U.S. Sen. Edward M. Kennedy has a malignant brain tumor, doctors treating him at Massachusetts General Hospital said Tuesday.
Kennedy, 76, was hospitalized Saturday morning after suffering a seizure at his family's compound at Hyannisport, Massachusetts.
"Preliminary results from a biopsy of the brain identified the cause of the seizure as a malignant glioma in the left parietal lobe," according to a hospital statement.
Malignant glioma is the most common primary brain tumor, accounting for more than half of the 18,000 primary malignant brain tumors diagnosed each year in the United States, according to the National Cancer Institute.
A tumor in that area of the brain could affect Kennedy's ability to speak and understand speech, as well as the strength on the right side of his body, CNN's Dr. Sanjay Gupta said.
The parietal lobes are also responsible for interpreting signals from parts of the brain that focus on vision, hearing, motor skills, sensory input and memory, according to the American Association of Neurological Surgeons.
The usual course of treatment for Kennedy's type of tumor includes radiation and chemotherapy, said Dr. Lee Schwamm, vice chairman of the Department of Neurology at Massachusetts General Hospital, and Dr. Larry Ronan, primary care physician.
Doctors said Kennedy would remain in the hospital for the next few days while they determine a proper course of treatment.
Friends and colleagues who spoke to Kennedy since he was hospitalized Saturday said he was alert and in good spirits.
As politicians across party lines reflected on Kennedy's contributions to the U.S. Senate, where he has represented Massachusetts since 1962, many cited his fighting spirit.
"Everybody needs to pull for him and his family and remember this guy is one unbelievable fighter," Kerry said. "He is determined to fight this because he wants to continue to fight for the people of Massachusetts. He wants to continue fighting for the things he believes here in the U.S. Senate."
Sen. Barack Obama, the front-runner for the Democratic presidential nomination, described Kennedy as a "giant" of the Senate.
"I think you can argue that I would not be sitting here as a presidential candidate had it not been for some of the battles that Ted Kennedy has fought," Obama told CNN's Wolf Blitzer.
"He is somebody who battled for voting rights and civil rights when I was a child. I stand on his shoulders," said Obama, who was waiting for the results of primaries in Kentucky on Tuesday.
Sen. Hillary Clinton, who is also competing for the Democratic nomination, said Kennedy's courage and resolve made him one of the greatest legislators in Senate history.
"He's a fighter. There isn't anybody like him who gets up and goes out and does battle on behalf of all of us every single day," Clinton said Thursday. "I know he's a fighter when it comes to the challenges he's facing right now."
Sen. John McCain, an Arizona Republican who is the GOP's presumptive presidential nominee, also offered his thoughts and prayers for Kennedy's family.
"I have described Ted Kennedy as the last lion in the Senate. And I have held that view because he remains the single most effective member of the Senate," McCain said from his campaign bus, the Straight Talk Express, in Florida. Video Watch McCain discuss Kennedy's contributions to the U.S. Senate »
President Bush said in a statement that he was saddened by the news and would keep the senator in his prayers.
"Laura and I are concerned to learn of our friend Sen. Kennedy's diagnosis. Ted Kennedy is a man of tremendous courage, remarkable strength and powerful spirit. Our thoughts are with Sen. Kennedy and his family during this difficult period," he said.
Kennedy had surgery in October to clear his carotid artery in hopes of preventing a stroke. But, in recent days, the powerful Democrat appeared in fine health.
On Friday, he took part in a ribbon-cutting ceremony for a maritime learning center in New Bedford, Massachusetts.
He suffers chronic back pain from injuries suffered in a plane crash in 1964.
Kennedy is one of only six senators in U.S. history to serve more than 40 years. He is known as a liberal champion of social issues such as health care, family leave and the minimum wage.
Senate Democrats and Republicans were in their weekly closed policy lunches in the Capitol when news of Kennedy's diagnosis broke.
"Ted Kennedy has spent his life caring for those in need. Now it's time for those who love Ted and his family to care for them and join in prayer to give them strength," Sen. Dick Durbin, D-Illinois, a close friend of Kennedy's, said in a statement.
Ted!
maybe Ted learned about deaf from my daddy?? 
cuz i have deaf brother and two deaf cousins too 