Warren Buffett, the billionaire founder of Berkshire Hathaway, disclosed on Tuesday that he has stage-one prostate cancer. "Grade one tumours are considered the least aggressive in behaviour and typically the slowest growing," said Dr Karen Thornton, a New York-based physician. The chief executive of the Omaha, Nebraska-based investment company was diagnosed last week after which he had additional medical tests, he said in a statement. The cancer has not spread to other parts of his body, he added. In his open letter, Mr Buffett said he would begin a two-month treatment of daily radiation from mid-July and would inform shareholders of any changes in his health. Mr Buffett said undertaking the treatment would restrict his travel during that period but it would not otherwise change his daily routine. Mr Buffett said in his most recent annual shareholder letter that Berkshire's board had chosen a candidate to take over from him as chief executive of the candy-to-cargo-train conglomerate as he prepares investors for an eventual transition. Neither the company nor Mr Buffett has identified that person or the two strong back up candidates. He has said his son Howard would maintain the company's culture in a non-executive chairman role and he has hired two former hedge-fund managers to help oversee investments. In three week's Berkshire will hold its annual meeting, which draws more than 40,000 shareholders to its headquarters in Omaha. Mr Buffett and Charlie Munger, his octogenarian vice-chairman, each year entertain the crowds with their thoughts on the economy and investing, and have maintained that they have no plans to step aside. Shares in Berkshire Hathaway fell 1.8 per cent in after-hours trading. The widely held Class B shares are up 5.9 per cent year-to-date.