Microsoft co-founder Paul Allen has been diagnosed with non-Hodgkin's lymphoma.
In a memo sent to employees, the chief executive of Mr Allen's investment firm says the 56-year-old Allen received the diagnosis this month and had begun chemotherapy.
The chief executive, Jody Patton, noted that doctors said Mr Allen had a relatively common form of the disease - and that Mr Allen survived Hodgkin's disease in the 1980s.
Ms Patton wrote that Mr Allen "is optimistic he can beat this, too".
Mr Allen founded Microsoft with Bill Gates in 1975.
Since leaving the company he has become a prolific investor in real estate, technology companies and sports teams.
He owns football's Seattle Seahawks and basketball's Portland Trail Blazers.