BOSTON -- Sen. Edward M. Kennedy was diagnosed with a malignant brain tumor Tuesday after the 76-year-old Democrat suffered a seizure Saturday at his Cape Cod home and was hospitalized at Massachusetts General Hospital.

Video: Diagnosis | Survival Rate | Lawmakers React

Doctors said that preliminary biopsy results showed a malignant glioma in the left parietal lobe -- a section of the brain that governs sensation and plays a role in movement and language.

"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," said a joint statement issued by Dr. Lee Schwamm, vice chairman of the Department of Neurology at Massachusetts General Hospital and Dr. Larry Ronan, Kennedy's primary care physician.

Doctors said that the senator has had no further seizures, remains in good overall condition and is up and walking around the hospital.

Kennedy will remain at Massachusetts General Hospital for the next couple of days. His wife, Vicki Kennedy, and his children have been with him every day since he was admitted to the hospital. Kennedy's son, Rep. Patrick Kennedy, released a statement through his spokesman Tuesday saying he was "hopeful his father will beat this and be back at it. It is definitely a medical challenge that he can get through."

The Associated Press released photos Tuesday of the senator laughing with family members as he sat in a family room at Massachusetts General Hospital. Kennedy was photographed smiling after he receive a gift basket from comedian Whoopi Goldberg with a card that read, "Get out of there now."

Sen. John Kerry offered words of support and said that Kennedy was a fighter and would get through this trying time with the help of his family and friends.

"Ted Kennedy and the Kennedy family have faced adversity more times and more instances with more courage and more determination and more grace than most families ever have to face such a situation once. Every one of us knows what a big heart this fellow has. He's helped millions and millions of people in so many ways at so many different times -- from the Legislation on the floor to the most personal when he would call you and help arrange a discussion with a bunch of doctors to talk about a wife who was sick or a child or any number of things. Now, everybody needs to do that on behalf of Ted," Kerry said.

Glioma is an aggressive form of brain cancer, in which the average survival rate can range from less than one year to about five years. About 20,000 people are diagnosed with this type of cancer, and half die in 18 months, according to Dr. Timothy Johnson.

Surgery can be an option for some types, but Johnson said that doctors have ruled out surgery for Kennedy and that he would likely be treated with chemotherapy and radiation.

"In many cases, seizure is the very first sign of a brain tumor. In an adult, a first-time seizure, is a brain tumor until proven otherwise, and unfortunately, that is what it turned out to be in this case," Johnson said. "In more advanced stages of a brain tumor, obviously, it can affect all kinds of issues in terms of sensation and movement, cognition, ability to speak depending on the location and the extension of the tumor."

Kennedy, the Senate's second-longest serving member, was re-elected to the Senate in 2006, and is not up for election again for another four years. State law requires a special election for the seat between 145 and 160 days after the vacancy, were he to resign or die in office.

"I think Ted Kennedy is irreplaceable. There will never be anyone who can fill Ted Kennedy's shoes. I think he is, perhaps, the one and only we will see in our lifetimes in terms of someone who has almost spent 50 years in the Senate, has passed more legislation and accomplished more things than most senators do combined in their lifetime," political analyst Mary Anne Marsh said.

Among the potential candidates for a Senate vacancy could be Massachusetts Attorney General Martha Coakley, Rep. Ed Markey, former Rep. Joe Kennedy and Vicki Kennedy on the Democratic side. Former Massachusetts Gov. Mitt Romney or former Lt. Gov. Kerry Healey could be potential candidates on the Republican side.