In his note just released by the company, Buffett says he was first told about the cancer last Wednesday.
After a CAT scan and bone scan the next day, and an MRI today, Buffett went public, even though his doctors tell him the condition is "not remotely life threatening or even debilitating in any meaningful way" and that the latest tests show "no incidence of cancer elsewhere in my body."
Buffett promises to let shareholders know "immediately" if his health changes, acknowledging that "eventually, of course, it will; but I believe that day is a long way off."
NBC News Chief Science Correspondent Robert Bazell agrees, telling us the "odds are overwhelming that Mr. Buffett will live to die of some other cause." He notes that many men Buffett's age elect not to have any treatment at all, as prostate cancer usually grows very slowly. Says Bazell, "He's in good shape."
Buffett says he will start two months of daily radiation treatments starting in mid-July. That will allow him to attend Allen & Co.'s annual Sun Valley retreat early that month.
Investors do not appear to be very concerned. As of 6pm Eastern, about an hour after the news release, Berkshire Class B shares were down just 1.5 percent to $79.55 in after-hour trading. The 52-week low on the stock is $65.35, set last September.
Buffett fan and Berkshire shareholder Whitney Tilson of T2 Partners tells Fast Money he's not changing his positive view on Berkshire's stock at all, in part because his "conservative" valuation of the company already doesn't include a "Buffett premium."
Investor Doug Kass, on the other hand, says he's rethinking his position. "The problem with this announcement is that the calculation of the company’s intrinsic value is impacted. The upside reward is now reduced... Valuations must now be adjusted."
Buffett's speed in disclosing his condition is a sharp contrast to the decision by Steve Jobs and Apple to delay or withhold release of details of the cancer that eventually took his life.
In a live interview with CNBC in June, 2009, Buffett backed criticism of the company for not immediately disclosing that Jobs had received a liver transplant several months earlier:
"If I have any serious illness, or something coming up of an important nature, an operation or anything like that, I think the thing to do is just tell the American, the Berkshire shareholders about it. I work for 'em. Some people might think I'm important to the company. Certainly Steve Jobs is important to Apple. So it's a material fact. Whether he is facing serious surgery or not is a material fact. Whether I'm facing serious surgery is a material fact."
Buffett reaffirms that the person, as before, does not know that he is the stand-by successor.
Email comments to firstname.lastname@example.org