OKLAHOMA CITY (AP) - Sen. Tom Coburn has announced he will resign at the end of the current session of Congress, nearly two years before his term is scheduled to end.
The decision comes just months after the two-term Republican senator was diagnosed with a recurrence of prostate cancer, but the 65-year-old said in a statement late Thursday that his health wasn't the reason.
"Carolyn and I have been touched by the encouragement we've received from people across the state regarding my latest battle against cancer," Coburn said, referring to his wife. "But this decision isn't about my health, my prognosis or even my hopes and desires.
"As a citizen, I am now convinced that I can best serve my own children and grandchildren by shifting my focus elsewhere. In the meantime, I look forward to finishing this year strong."
Coburn, nicknamed "Dr. No." for his voting record in the Senate, was supposed to serve through 2016. Instead, he'll step down in January 2015. He had already vowed not to seek a third term.
Senate Republican Leader Mitch McConnell released a statement Thursday describing Coburn as "one of the most intelligent, principled and decent men in modern Senate history."
"When it comes to the transcendent debate over the size and cost of government, Tom Coburn is simply without peer," McConnell, R-Ky., said. "No one has done more to awaken Americans to the threat posed by a government that chronically spends more than it takes in, and no one has worked harder at finding a solution."
Known as a conservative maverick during his three terms in the U.S. House in the 1990s, Coburn continued that role after being elected to the Senate in 2004. A fierce critic of what he described as excessive government spending, Coburn was most vocal about opposing the earmarking of special projects.
His office routinely produced reports on wasteful spending, like a 37-page report in 2011 dubbed "Subsidies of the Rich and Famous" that detailed nearly $30 billion spent annually on government tax breaks and federal grant programs for millionaires.
And late last year, Coburn was among a group of senators who released the findings of a two-year probe into alleged abuses in how Social Security disability benefits were approved at a federal Office of Disability Adjudication and Review in West Virginia. The study detailed inappropriate conduct between Social Security law judges, a law firm, and doctors in approving benefits, and an apparent lack of oversight from the agency.
Coburn's thwarting of legislation that Democrats consider worthy has often frustrated Senate Majority Leader Harry Reid, who declared in 2008: "You cannot negotiate with Coburn. It's just something you learn over the years is a waste of time."
Coburn's resignation is certain to draw the interest of a deep bench of ambitious Republicans in Oklahoma, and the GOP will be heavily favored to retain control of the seat. Among the Republicans mentioned as possible contenders are U.S. Reps. Tom Cole, Frank Lucas, Jim Bridenstine and James Lankford, along with Attorney General Scott Pruitt.
State law requires the governor to call a special election in the case of a vacancy.
Coburn was treated for prostate cancer in 2011, and has battled numerous health issues in past years.
He revealed in 2003 he'd been diagnosed with colon cancer and had undergone surgery and chemotherapy. He told a reporter at the time, "you should be writing about Medicaid and Medicare instead of my health."
Coburn also was treated for malignant melanoma in 1975, and had a benign tumor removed from his pituitary gland in 2007. He also was tested for an irregular heartbeat in 2008.