Douglas, 65, who is married to another Hollywood A-lister, British actress Catherine Zeta-Jones, only recently revealed that he had been diagnosed with throat cancer when he returned to the United States from a family holiday three weeks ago.
But he had not mentioned the seriousness of the disease in his earlier interview with People magazine.
He told Letterman Tuesday: "I am head and neck, I am above the neck, so nothing's gone down and the expectations are good.
"You like to be down at stage one but the big thing you worry about is it spreading."
The son of screen legend, Kirk Douglas, who is now 93, Michael Douglas said he had been suffering from throat problems for several months.
"I went through a litany of doctors and tests and they didn't find anything and then I had a great summer after some other personal adversities," he told Letterman.
He said he had spent "a wonderful summer with Catherine and the kids in Spain. We went to Russia, St. Petersburg, which is fantastic."
"I came back and a guy said 'Let me have a look'. All happened within three weeks. They got a biopsy and analyzed it."
Douglas, who has two young children with Zeta-Jones, said he was undergoing radiation and chemotherapy.
"The percentages are very good. I would hate to say, but right now, it looks like it should be 80 percent, and with certain hospitals and everything, it does improve."
Douglas is one of the pillars of the Hollywood film industry having starred in more than 40 films, including such hits as "Fatal Attraction" (1988), "Wall Street" (1988), "War of the Roses" (1990), "Basic Instinct" (1992) and "Traffic" (2001).
Douglas's latest film, the sequel to the 1987 box office hit "Wall Street" called "The Money Never Sleeps," directed by Oliver Stone, is due to hit movie theaters in the United States later this month.
Douglas has a son from an earlier marriage, Cameron Douglas, who was sentenced in April to five years in prison for drug-trafficking.
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