Image caption Warren Buffett said there was "no incidence of cancer" elsewhere in his body

Billionaire investor Warren Buffett has said in a letter to shareholders that he has been diagnosed with stage one prostate cancer.

The Berkshire Hathaway boss said the cancer, detected in a routine test, was "not remotely life threatening".

Mr Buffett, 81, said he would begin a two-month course of daily radiation treatment from mid-July.

He was diagnosed on 11 April and has since undergone a CAT scan, bone scan and MRI, he said.

According to the National Cancer Institute , a federal agency, the five-year survival rate for US prostate cancers found at an early, localised stage is nearly 100%.

Buffett's successor picked

It is the most common cancer in men, with more than 241,000 new cases expected in the US this year.

In his letter, Mr Buffett said he felt "great - as if I were in my normal excellent health - and my energy level is 100 percent".

"I will let shareholders know immediately should my health situation change," he added. "Eventually, of course, it will. But I believe that day is a long way off."

In February, Mr Buffett told shareholders that Berkshire Hathaway's board had already chosen someone to succeed him as chief executive - but not yet - and that there were two back-up candidates.

The tycoon says the unnamed chosen successor and back-ups have not been told they are in line to take over the company.

Mr Buffett has previously said his son Howard, a member of Berkshire's board, would make an ideal chairman.

With his personal wealth estimated at $44bn (£27bn), Warren Buffett is listed by Forbes magazine as the world's third richest person.

His name has been in the headlines this week in Washington, where lawmakers have been considering the Buffett Rule, a proposal by President Barack Obama to increase taxes on the wealthy.

It was inspired by Mr Buffett's assertion that his secretary should not be paying a higher rate of tax than he does.