OMAHA, Neb. — Warren Buffett told his company's shareholders in an open letter Tuesday that he has been diagnosed with early-stage prostate cancer.

The 81-year-old billionaire investor and CEO of Berkshire Hathaway Inc. said his condition is "not remotely life-threatening" or debilitating. He said he and his doctors have decided on a two-month treatment plan that is to begin in mid-July.

"I feel great – as if I were in my normal excellent health," Buffett said in the letter. "And my energy level is 100 percent. I discovered the cancer because my PSA level (an indicator my doctors had regularly checked for many years) recently jumped beyond its normal elevation and a biopsy seemed warranted."

Buffett said he was diagnosed April 11 and has received tests including a CAT scan, a bone scan and an MRI.

Buffett is known for a no-nonsense approach to investing. He is one of the world's richest men and, in recent years, has become one of its most generous philanthropists.

Buffett's stake in Berkshire Hathaway was more than $43 billion as of December.

Although his investment success has made Buffett a Wall Street icon, he still lives and works in his hometown of Omaha in a house he bought in 1958.

Some 240,000 men in the U.S. are diagnosed with prostate cancer each year.

Many prostate cancer patients with slow-growing tumors can live their whole lives without symptoms or treatment, according to the American Cancer Society. Many die of something else before the cancer kills them.

Buffett concluded his letter with a nod to that fact.

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