Douglas, 68, who is in remission, said, "Things had been going good for me for a long time. I was ready for some karmic retribution."
He found out he had the disease in 2010 and lost more than 5lb fighting it, reported Sun Online.
The veteran is to star as late entertainer Liberace in movie "Behind the Candelabra" with Matt Damon.
"It feels great to be back at work," he said.
Douglas' wife Catherine Zeta Jones, 43, is currently in a clinic with bipolar disorder.