The governor's office made the announcement this afternoon. From the Sacramento Bee:
The governor's office described the condition as a "localized prostate cancer" and said Brown is continuing to work a full schedule while being treated with a short course of radiation.
It released a statement from Eric Small, Brown's oncologist at University of California San Francisco.
"Fortunately, this is early stage localized prostate cancer, which is being treated with a short course of conventional radiotherapy," Small said in the statement. "The prognosis is excellent, and there are not expected to be any significant side effects."
Brown's office said the treatment is expected to be completed the week of Jan. 7.
Last year Brown, who is 74, had a cancerous growth removed from the right side of his nose.