You can't say "some people have all the luck" when you see Paul Allen's mansion on the shore of Mercer Island, his airplanes, superyachts and vast land holdings in Seattle.

The son of a Seattle librarian became one of the richest people in the world when he and childhood pal Bill Gates struck it rich after starting Microsoft in 1975.

But today Allen's sister disclosed that he's been diagnosed with non-Hodgkin's lymphoma, a cancer similar to the one he battled 25 years ago, a life-changing experience that prompted him to retire early from Microsoft.

The cancer follows a tough bout with heat disease that sidelined Allen, 56, earlier this year and led to a heart valve replacement. Details were largely secret until he confided in an Oregonian sports columnist who had seen Allen accompanied by a doctor to Blazers games.

"I'm fine, finally," Allen told John Canzano in September. "I'm much, much better. I hit a few bumps in the road."

Now he's hit another bump.

Allen's sister, Jody Allen, notified employees of his Seattle holding company that the cancer returned earlier this month.

"He received the diagnosis early this month and has begun chemotherapy. Doctors say he has diffuse large B-cell lymphoma, a relatively common form of lymphoma," she said in the e-mail, which was disclosed by Allen's spokesman.

"This is tough news for Paul and the family. But for those who know Paul's story, you know he beat Hodgkin's a little more than 25 years ago and he is optimistic he can beat this, too," she wrote.

"Paul is feeling OK and remains upbeat. He continues to work and he has no plans to change his role at Vulcan. His health comes first, though, and we'll be sure that nothing intrudes on that."

Allen and Patton were not available for interviews. Their spokesman, David Postman, said Allen's still active at Vulcan.

"He remains just as involved as always," he said.

Gates issued a statement of support.

"Melinda and I have Paul and his family in our thoughts and prayers," he said. "Paul is among my closest friends, and I know to him be a strong and resilient individual."

Lymphoma is a cancer that starts in cells called lymphocytes in the body's immune system, according to the American Cancer Society.

Non-Hodgkin's "is a fast growing lymphoma, but it often responds well to treatment with chemotherapy," the society's Web site says. "Overall, about 3 out of 4 people will have no signs of disease after initial treatment, and about half of all people with this lymphoma are cured with therapy."

Risk factors include a weakened immune system, which can result from drugs taken during a transplant procedure.

Allen's also been under considerable stress over the past year as his biggest investment, St. Louis-based Charter Communications, filed for bankruptcy with $21.7 billion in debt.