Republican senator Tom Coburn announced tonight that he will be retiring at the end of this session of Congress, two years before the end of his term.

Coburn, from Oklahoma, announced in November that his prostate cancer had returned (he's also fought melanoma and colon cancer) and he would undergo chemotherapy. He was said last week to be considering retiring before his term was up in January 2017. He was first elected to the Senate in 2004.

But in his statement about his decision, Coburn said "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."

He didn't elaborate on that much to News OK, simply saying: "I've had a lot of changes in my life. This is another one."

Coburn will be the eighth senator to retire at the end of this session, joining Max Baucus (D-MT), Saxby Chambliss (R-GA), Tom Harkin (D-IA), Mike Johanns (R-NE), Tim Johnson (D-SD), Carl Levin (D-MI) and John Rockefeller (D-WV).