The 56-year-old Allen was diagnosed with diffuse large B-cell lymphoma earlier this month, according to a letter sent by his sister, Jody Allen, to employees of his investment company Vulcan. It is a non-Hodgkin's form of the disease. Allen left Microsoft in 1983 after being diagnosed with Hodgkin's disease.
"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," Jody Allen said in the e-mail, sent Monday.