Former Pennsylvania Senator Arlen Specter died on Sunday from complications of non-Hodgkins Lymphoma, according to the AP.

He was 82.

A longtime moderate Republican, Specter made headlines in 2009 when he announced that he was switching to the Democratic Party. He left office in 2011 after being defeated in the Democratic primary.

In 2005, Specter announced that he was being treated for non-Hodgkins Lymphoma. He recovered, but the illness resurfaced in 2008 and again in 2012. He was hospitalized in August.

The AP's full obituary is below.

HARRISBURG, Pa. — Former U.S. Sen. Arlen Specter, the outspoken Pennsylvania centrist whose switch from Republican to Democrat ended a 30-year career in which he played a pivotal role in several Supreme Court nominations, died Sunday. He was 82.

Specter, who announced in late August that he was battling cancer, died at his home in Philadelphia from complications of non-Hodgkins lymphoma, said his son Shanin. Over the years, Arlen Specter had fought two previous bouts with Hodgkin's disease, overcome a brain tumor and survived cardiac arrest following bypass surgery.

Specter rose to prominence in the 1960s as an aggressive Philadelphia prosecutor and as an assistant counsel to the Warren Commission, developing the single-bullet theory that posited just one bullet struck both President Kennedy and Texas Gov. John Connally – an assumption critical to the argument that presidential assassin Lee Harvey Oswald acted alone. The theory remains controversial and was the focus of Oliver Stone's 1991 movie "JFK."

In 1987, Specter helped thwart the Supreme Court nomination of former federal appeals Judge Robert H. Bork – earning him conservative enemies who still bitterly refer to such rejections as being "borked."

But four years later, Specter was criticized by liberals for his tough questioning of Anita Hill at Clarence Thomas' Supreme Court nomination hearings and for accusing her of committing "flat-out perjury." The nationally televised interrogation incensed women's groups and nearly cost him his seat in 1992.

Specter, who had battled cancer, was Pennsylvania's longest-serving senator when Democrats picked then-U.S. Rep. Joe Sestak over him in the 2010 primary, despite Specter's endorsements by President Barack Obama and other Democratic leaders. Sestak lost Specter's seat to conservative Republican Rep. Pat Toomey by 2 percentage points.

A political moderate, Specter was swept into the Senate in the Reagan landslide of 1980.

He took credit for helping to defeat President Clinton's national health care plan – the complexities of which he highlighted in a gigantic chart that hung on his office wall for years afterward – and helped lead the investigation into Gulf War syndrome. Following the Iran-Contra scandal, he pushed legislation that created the inspectors general of the CIA.

As a senior member of the powerful Appropriations Committee, Specter pushed for increased funding for stem-cell research, breast cancer and Alzheimer's disease, and supported several labor-backed initiatives in a GOP-led Congress. He also doggedly sought federal funds for local projects in his home state.

The former Democrat was not shy about bucking fellow Republicans.

In 1995, he launched a presidential bid, denouncing religious conservatives as the "fringe" that plays too large a role in setting the party's agenda. Specter, who was Jewish, bowed out before the first primary because of lackluster fundraising.

Despite his tireless campaigning, Specter's irascible independence caught up with him in 2004. Specter barely survived a GOP primary challenge by Toomey by 17,000 votes of more than 1.4 million cast. He went on to easily win the general election with the help of organized labor, a traditionally Democratic constituency.

Specter startled fellow senators in April 2009 when he announced he was switching to the Democratic side, saying he found himself "increasingly at odds with the Republican philosophy." Earlier in the year, he had been one of only three Republicans in Congress – and the only one facing re-election in 2010 – who voted for President Barack Obama's economic stimulus bill.

He also said he had concluded that his chance of defeating a GOP challenger in the 2010 party primary was bleak. But he said the Democrats couldn't count on him to be "an automatic 60th vote" to give the party a filibuster-proof majority.

Specter outspent Sestak, a retired Navy vice admiral, but Sestak attacked him as a political opportunist who switched parties to save his job. A memorable campaign ad used Specter's own words against him: "My change in party will enable me to be re-elected."

Specter was diagnosed in February 2005 with stage IV Hodgkin's disease, a cancer of the lymphatic system. Announcing the diagnosis with his trademark doggedness, Specter said: "I have beaten a brain tumor, bypass heart surgery and many tough political opponents and I'm going to beat this, too."

He wrote of his struggle in a 2008 book, "Never Give In: Battling Cancer in the Senate," saying he wanted to let others facing similar crises "ought to know they are not alone."

Cancer handed him "a stark look at mortality" and an "added sense of humility," Specter told The Associated Press.

Intellectual and stubborn, Specter played squash nearly every day into his mid-70s and liked to unwind with a martini or two at night. He took the lead on a wide spectrum of issues and was no stranger to controversy.

Born in Wichita, Kan., on Feb. 12, 1930, Specter spent summers toiling in his father's junkyard in Russell, Kan., where he knew another future senator – Bob Dole. The junkyard thrived during World War II, allowing Specter's father to send his four children to college.

Specter left Kansas for college in 1947 because the University of Kansas, where his best friends were headed, did not have Jewish fraternities. He graduated from the University of Pennsylvania in 1951 and Yale law school in 1956. He served in the Air Force from 1951 to 1953.

Friends say his childhood circumstances made him determined, tough and independent-minded. Specter considered his father's triumphs the embodiment of the American dream, a fulfillment that friends say drove him to a career in public life.

He entered politics as a Democrat in Philadelphia in the early 1960s, when he was an assistant district attorney who sent six Teamsters officials to jail for union corruption.

After working on the Warren Commission, he returned to Philadelphia and challenged his boss, James Crumlish, for district attorney in 1965. Specter ran as a Republican and was derided by Crumlish as "Benedict Arlen." But Crumlish lost to his protege by 36,000 votes.

It was to be the last time until 1980 that Specter would win an election to higher office, despite three attempts – a 1967 bid for Philadelphia mayor, a 1976 loss to John Heinz for Senate and a 1978 defeat by Dick Thornburgh for governor.

Specter lost re-election as district attorney in 1973 and went into private practice. Among his most notorious clients as a private attorney was Ira Einhorn, a Philadelphia counterculture celebrity who killed his girlfriend in 1977.

Finally, in 1980, Specter won the Senate seat vacated by retiring Republican Richard Schweiker, defeating former Pittsburgh Mayor Pete Flaherty.

After leaving the Senate in January 2011, the University of Pennsylvania Law School announced Specter would teach a course about Congress' relationship with the Supreme Court, and Maryland Public Television launched a political-affairs show hosted by the former senator.

A funeral was scheduled for Tuesday in Penn Valley, Pa., and will be open to the public, followed by burial in Huntingdon Valley, Pa.

He is survived by his wife, Joan, and two sons, Shanin and Steve, and four granddaughters.

___

Associated Press writers Ron Todt in Philadelphia and Lara Jakes contributed to this report.

UPDATE: Sunday, 2:37 p.m.-- President Obama issued the following statement on Specter's passing:

Arlen Specter was always a fighter. From his days stamping out corruption as a prosecutor in Philadelphia to his three decades of service in the Senate, Arlen was fiercely independent – never putting party or ideology ahead of the people he was chosen to serve. He brought that same toughness and determination to his personal struggles, using his own story to inspire others. When he announced that his cancer had returned in 2005, Arlen said, "I have beaten a brain tumor, bypass heart surgery and many tough political opponents and I'm going to beat this, too." Arlen fought that battle for seven more years with the same resolve he used to fight for stem-cell research funding, veterans health, and countless other issues that will continue to change lives for years to come. Michelle and I send our thoughts and prayers to Joan and the rest of the Specter family.

UPDATE: Sunday, 7:05 p.m.-- Vice President Joe Biden released a statement mourning the loss of Specter:

Jill and I are deeply saddened. Arlen Specter was a great Senator who lived his life the way he died, with dignity and courage. He was my friend and I admired him a great deal.

For over three decades, I watched his political courage accomplish great feats and was awed by his physical courage to never give up. Arlen never walked away from his principles and was at his best when they were challenged.

Jill and I are thinking of Joan at the moment – she was an incredible partner through his life journey. Our hearts go out to Shanin and Stephen and all who were deeply touched by his life.

Also on HuffPost:

Loading Slideshow...
  • Arlen Specter

    In this June 6, 2009 file photo, Pennsylvania Sen. Arlen Specter, D-Pa., addresses the Pennsylvania Democratic State Committee Meeting in Pittsburgh. Specter, Pennsylvania's longest serving U.S. Senator, is hosting a pilot episode of a public affairs show that airs Friday, Jan. 13, 2012 on Maryland Public Television. (AP Photo/Gene J. Puskar, File)

  • Arlen Specter

    FILE - In this June 6, 2009 file photo, Pennsylvania Sen. Arlen Specter, D-Pa., addresses the Pennsylvania Democratic State Committee Meeting in Pittsburgh. Specter, Pennsylvania's longest serving U.S. Senator, is hosting a pilot episode of a public affairs show that airs Friday, Jan. 13, 2012 on Maryland Public Television. (AP Photo/Gene J. Puskar, File)

  • Arlen Specter

    FILE - Sen. Arlen Specter, R-Pa. is seen in Philadelphia, in this Nov. 7, 2008 file photo. The longtime Pennsylvania senator performed at an open-mic night at the Helium Comedy Club in Philadelphia on Tuesday, Dec. 27, 2011 continuing a post-politics foray into standup. (AP Photo/Matt Rourke, file)

  • The 33rd Annual Kennedy Center Honors

    WASHINGTON, DC - DECEMBER 05: Arlen Specter poses for photos during the 33rd Annual Kennedy Center Honors at the Kennedy Center Hall of States on December 5, 2010 in Washington, DC. (Photo by Kris Connor/Getty Images)

  • National Museum of American Jewish History opening gala hosted by Jerry Seinfeld and Bette Midler

    PHILADELPHIA - NOVEMBER 13: Arlen Specter (R) attends the National Museum of American Jewish History opening gala hosted by Jerry Seinfeld and Bette Midler at National Museum of American Jewish History on November 13, 2010 in Philadelphia, Pennsylvania. (Photo by Mike Coppola/Getty Images for National Museum of American Jewish History)

  • Rick Santorum, Arlen Specter, Edward G. Rendell

    FILE - In this July 7, 2005 file photo, Sen. Rick Santorum, R-Pa., right, and Sen. Arlen Specter, R-Pa. , and Pennsylvania Gov. Edward G. Rendell, left, testify on Capitol Hill, Thursday in Washington. With the Iowa presidential caucuses on Tuesday, Santorum is hoping to spring a surprise showing by casting himself as the only "consistent conservative" among his GOP rivals. He's been stuck at the back of the pack for months, but he's steadily visited every Iowa county and pressed for support from Republicans with doubts about the conservative credentials of other candidates, especially Mitt Romney and Newt Gingrich. (AP Photo/Lawrence Jackson, File)

  • Senator Arlen Specter walks across the t

    Senator Arlen Specter walks across the tarmac after stepping off Air Force One on June 2, 2010 upon return to Andrews Air Force Base in Maryland. Specter was travelling with US President Barack Obama who was returing to Washington after a visit to to Pittsburgh, Pennsylvania where spoke on the economy at Carnegie Mellon University. Specter, who quit the Republican Party to become a Democrat a year ago, lost his bid for a new term last month. AFP PHOTO / Mandel NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)

  • Arlen Specter Loses Senate Bid In Democratic Primary

    PHILADELPHIA - MAY 18: (L-R) Sen. Arlen Specter (D-PA) concedes defeat at a primary night gathering of supporters and staff with his wife Joan Specter and son Shanin Specter May 18, 2009 in Philadelphia, Pennsylvania. Specter, a five-term Senator who switched his political affiliation a year ago, was defeated by Rep. Joe Sestak in the Democratic primary. (Photo by Win McNamee/Getty Images)

  • Arlen Specter Campaigns In Philadelphia On Primary Day

    PHILADELPHIA - MAY 18: Sen. Arlen Specter (D-PA) talks with reporters while touring the site of his primary night gathering for staff and supporters May 18, 2010 in Philadelphia, Pennsylvania. Specter is fighting a close campaign against Rep. Joe Sestak for the Democratic Senate nomination as voters go to the polls today. (Photo by Win McNamee/Getty Images)

  • Arlen Specter Campaigns In Philadelphia On Primary Day

    PHILADELPHIA - MAY 18: Sen. Arlen Specter (D-PA) answers questions from the press with his wife Joan while campaigning at the 4th Street Deli May 18, 2010 in Philadelphia, Pennsylvania. Specter is fighting a close campaign against Rep. Joe Sestak for the Democratic Senate nomination as voters go to the polls today. (Photo by Win McNamee/Getty Images)

  • Senate Judiciary Committee Holds Hearing On Steriods Usage

    WASHINGTON - SEPTEMBER 29: Senate Judiciary Committee's Crime and Drugs Subcommittee Chairman Arlen Specter (D-PA) delivers an opening statement during a hearing on 'Body Building Products and Hidden Steroids: Enforcement Barriers' on Capitol Hill September 29, 2009 in Washington, DC. The committee is considering drawing up legislation that would give the Food and Drug Administration the responsibility of screening dietary suppliments for illegal steroids before they can be marketed and sold. (Photo by Chip Somodevilla/Getty Images)

  • Sen. Arlen Specter Holds Health Care Town Hall Meeting

    KITTANNING, PA - AUGUST 13: Senator Arlen Specter (D-PA) speaks at at a town hall meeting on August 13, 2009 in Kittanning, Pennsylvania. Specter held the town hall meeting to speak with local residents about health care reform. (Photo by Jeff Swensen/Getty Images)

  • US Secretary of State Hillary Clinton la

    US Secretary of State Hillary Clinton laughs with Sen. Arlen Spector (D-PA) before her testimony at the Senate Appropriations Committee, on May 20, 2009 on Capitol Hill in Washington, DC. AFP PHOTO / Tim Sloan (Photo credit should read TIM SLOAN/AFP/Getty Images)

  • US Senator Arlen Specter speaks as US P

    US Senator Arlen Specter speaks as US President Barack Obama looks on April 29, 2009 in the Diplomatic Reception Room of the White House in Washington, DC. Specter, a veteran Republican senator from Pennsylvania, announced April 28, 2009 that he was switching to the Democratic party. AFP PHOTO/Mandel NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)

  • Obama Welcomes Specter to the Democratic Party

    WASHINGTON - APRIL 29: U.S. Sen. Arlen Specter (D-PA) speaks speaks during a press conference welcoming him to the Democratic Party at the White House on April 29, 2009 in Washington, DC. Obama expressed his support for Spector and his run for re-election as a democrat. (Photo by Ron Sachs-Pool/Getty Images)