Sen. Edward M. Kennedy, the liberal lion of the Democratic Party, walked out of a Boston hospital Wednesday morning, flashing a smile and patting his dogs Sunny and Splash, one day after learning his weekend seizure was caused by a cancerous brain tumor.

A square bandage atop the backside of his head was evidence of a biopsy performed on the Massachusetts senator that led doctors to their diagnosis.

Kennedy later arrived at the family's Hyannisport, Mass., compound, where he will confer over the Memorial Day weekend with family and doctors about his next course of action.

• Click here to view photos.

Hospital workers and well-wishers bade farewell to Kennedy with applause, which he acknowledged with a thumbs up. Before he and his wife, Vicki, got into a dark Chevrolet Suburban, he kissed his daughter, Kara — herself a cancer survivor — and his niece Caroline Kennedy, and embraced his son, Rep. Patrick Kennedy, D-R.I.

Kennedy departed with a wave as television news helicopters followed his 75-mile trip south. Along the way, he could be seen waving to nearby motorists from the front passenger seat of his SUV.

In a statement, doctors announced the senator was being released because he "has recovered remarkably quickly" from the brain biopsy.

"He's feeling well and eager to get started," said Dr. Lee Schwamm, a top neurologist at Massachusetts General, and Dr. Larry Ronan, Kennedy's primary care physician.

Doctors discovered the tumor after Kennedy, the sole surviving son of America's most storied political family, suffered a seizure last the weekend. The cancer diagnosis cast a pall over Capitol Hill, where the Massachusetts Democrat has served since 1962, and came as a shock to a family accustomed to sudden, calamitous news.

Some medical experts gave the 76-year-old senator less than a year to live.

Despite the bad news, a family confidante said Kennedy has given no thought to retirement.

"It's not even an option," the associate told The Boston Globe.

Kennedy reportedly has ordered his aides to get back to work, and one associate told the newspaper that he is attacking his diagnosis "as if he were mapping strategy to enact a piece of legislation."

In an e-mail sent to friends Tuesday, 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.

AUDIO: Click here to hear California Gov. Arnold Schwartzenegger talk about Sen. Ted Kennedy on FOX News Radio.

Kennedy's doctors at Massachusetts General Hospital said he had a malignant glioma in the left parietal lobe, a region of the brain that helps govern sensation, movement and language.

Seizures can be caused by a wide variety of things, some of them relatively minor. The finding of a brain tumor — and specifically a glioma, an especially lethal type — was about the worst possible news.

Kennedy's doctors said they are considering chemotherapy and radiation treatments. They did not mention surgery, a possible indication the tumor is inoperable.

"As a general rule, at 76, without the ability to do a surgical resection, as kind of a ballpark figure you're probably looking at a survival of less than a year," said Dr. Keith Black, chairman of neurosurgery at Cedars-Sinai Medical Center in Los Angeles.

"It's treatable but not curable. You can put it into remission for a while but it's not a curable tumor," said Dr. Suriya Jeyapalan, a neuroncologist at Beth Israel Deaconess Medical Center in Boston.

Vicki, Kennedy's wife since 1992, and his five children and stepchildren had been at his bedside.

"Obviously it's tough news for any son to hear," said Robin Costello, a spokeswoman for one of Kennedy's sons, Rep. Patrick Kennedy. "He's comforted by the fact that his dad is such a fighter, and if anyone can get through something as challenging as this, it would be his father."

Kennedy, the Senate's second-longest serving member, was re-elected in 2006 and is not up for election again until 2012. Were he to resign or die in office, state law requires a special election for the seat 145 to 160 days afterward.

Kennedy has left his stamp on a raft of health care, pension and immigration legislation during four decades in the Senate.

Senators of both parties heard about Kennedy's condition during their weekly, closed-door policy lunches, and some looked drawn or misty-eyed.

Sen. Robert Byrd, 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, my dear friend, I love you and I miss you."

"He's a fighter," said Sen. Chris Dodd, on ABC's "Good Morning America" Wednesday. "I wouldn't want to be that tumor. With Teddy Kennedy fighting back, you're in trouble."

In a statement, President George W. Bush saluted Kennedy as "a man of tremendous courage, remarkable strength and powerful spirit."

The Kennedy family has been frequently struck by tragedy. Kennedy's oldest brother, Joseph, died in a World War II plane crash; President John F. Kennedy was assassinated during in 1963; and Sen. Robert F. Kennedy was assassinated in 1968. The tragedies thrust "Uncle Teddy" into the role of surrogate parent to his brothers' children.

In 1980, Kennedy challenged Jimmy Carter for the Democratic presidential nomination. He eventually bowed out with a stirring speech in which he declared, "The cause endures, the hope still lives and the dream shall never die."

In 1969, Kennedy drove a car off a bridge on Chappaquiddick Island off Martha's Vineyard. The accident killed aide Mary Jo Kopechne. Kennedy at the time was married to his first wife, Joan, whom he later divorced. His failure to promptly report the accident, and questions about his relationship with the young woman, may have cost him the presidency.

Kennedy has been active for his age, maintaining an aggressive schedule on Capitol Hill and across Massachusetts. He has made several campaign appearances for Sen. Barack Obama.