(PTI): A former co-founder of US software giant Microsoft Corporation, Paul Allen, is undergoing treatment for non-Hodgkin’s lymphoma.

According to Allen’s sister, Jody, her brother is optimistic that he can regain his health once again, The Wall Street Journal reported. Non-Hodgkin’s lymphoma is a cancer of the lymphatic system.

“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,” she said.

Jody Allen is chief executive officer of Vulcan Inc., Allen’s investment firm.

In a statement, Microsoft’s other co-founder Bill Gates said, “Paul is among my closest friends, and I know him to be a strong and resilient individual.”

Twenty-five years ago, Allen won a battle with Hodgkin’s disease. That diagnosis was made before he left Microsoft, the Journal said.