Gov. Jerry Brown is being treated for prostate cancer, his administration said Wednesday, characterizing the condition as "localized" and unlikely to affect his work.

The governor, who is 74, is undergoing radiation, the administration said. His office said he is continuing to work while being treated, and released a statement from his oncologist at the University of California, San Francisco.

"Fortunately, this is early-stage, localized prostate cancer, which is being treated with a short course of conventional radiotherapy," said the doctor, Eric Small. "The prognosis is excellent, and there are not expected to be any significant side effects."

Prostate cancer is not uncommon in older men and responds well to treatment. Brown's office said treatment is expected to be completed the week of Jan. 7.

Brown underwent a procedure in April 2011 to remove skin cancer from his nose. In both cases the administration has closely guarded details of Brown's condition.

Officials on Wednesday declined to provide any information beyond what was included in a written statement, including when Brown was diagnosed or began treatment.

The governor himself has not spoken publicly about the cancer, and he did not mention it at a private lunch with business leaders in San Jose on Wednesday, said Carl Guardino, CEO of the Silicon Valley Leadership Group.

"He was his normal, vigorous, vital, funny, insightful, curious self," Guardino said. "He was completely focused. There was no distraction."

Brown, who is famously fit – jogging and challenging guests to pull-up contests, among other activities – mentioned lifting weights Wednesday morning, Guardino said.

A third-term governor, Brown, a Democrat, is widely expected to run for re-election in 2014. His political adviser, Steve Glazer, said he expects Brown to run and that the diagnosis will have no impact on his decision.

"He's in great health," Glazer said. "He's in great physical shape, and given the positive prognosis, it will have no effect."

Politicians often hesitate to talk about health conditions because the subject matter can accentuate one's frailty – or one's age.

Former Los Angeles Mayor Richard Riordan did not disclose that he had prostate cancer when he underwent radiation treatment while in office, only revealing it ahead of his run for governor in 2002.

Dan Schnur, who was director of Riordan's exploratory committee, said the campaign disclosed the cancer because "we thought it was important to voters not just to have the information, but to understand it."

"Ten or 11 years ago, cancer still had the potential to be a political scarlet letter for a candidate," said Schnur, director of the Jesse Unruh Institute of Politics at the University of Southern California. "We wanted voters to understand that it was a condition that could be treated and didn't pose any threat to his abilities to govern."

Like Schnur, Tony Quinn, a political analyst and former Republican legislative aide, said the diagnosis would have no effect on Brown "in this day and age."

"It does reinforce the fact that he's over 70," Quinn said. "But I think that in this day and age, if he decides to run for re-election, it's not going to have any effect on that because it's so common."

The National Cancer Institute says that one in six men will be diagnosed with prostate cancer at some time during their lives, and that more than 8 percent of men will develop prostate cancer between their 50th and 70th birthdays.