SACRAMENTO, Calif. – Gov. Jerry Brown is being treated for early stage prostate cancer but will stay on the job throughout his nearly four-week treatment, his office said Wednesday, calling the typically energetic 74-year-old chief executive’s prognosis “excellent.”

Brown’s office gave few details about his treatment or how Brown was found to be suffering from the second-most common cancer to afflict men, but said in a statement that he would undergo conventional radiotherapy until the week of Jan. 7 for what it called a “localized” cancer.

The three-term governor’s “prognosis is excellent, and there are not expected to be any significant side effects,” University of California, San Francisco oncologist Eric Small said in the statement. Small is Brown’s oncologist.

Brown’s spokesman Gil Duran declined further comment.

Localized prostate cancer means “the tumor is still contained within the prostate,” said Dr. Mark Litwin, chairman of the UCLA Department of Urology, who is not involved in Brown’s care. “Of course, that’s what you want because you can treat it much more effectively.”

For early stage prostate cancer, the typical radiation treatment is five days a week for four to five weeks, said Dr. Ralph de Vere White, urological oncologist and director of the University of California, Davis Comprehensive Cancer Center in Sacramento. Other oncologists said the treatments can sometimes last up to nine weeks.

Not all men who are diagnosed with the disease choose to undergo treatment, and doctors advise patients to consider the risks.