The 57-year-old actor, best known for his roles in Jaws 3 and U.K. medical drama Casualty, was diagnosed with bowel cancer in 2006 after complaining of stomach cramps while filming in Bristol, England.
He only disclosed the terrifying news to his wife of 25 years, Straw Dogs actress Susan George, and the pair kept the cancer a secret while MacCorkindale underwent surgery to remove a section of his bowel.
But just a year later (07), doctors admitted the disease had spread to his lungs and was incurable.
MacCorkindale has revealed medics have now given him just three years left to live.
He says, "It came as a complete bombshell. I thought I had beaten bowel cancer. The oncologist said I had lung cancer - me, who never smoked a cigarette my whole life and always tried to live a healthy lifestyle.
"We thought no one needed to know because, for the first year or so, we didn't think it was that serious. On a more practical level, showbusiness is a difficult place in which to work when people think you're sick. But the news has been slowly creeping out and at least this way we can tell the story in our own words."
And the actor is adamant he will continue fighting the disease. He adds, "I don't want people to think that I'm pale, losing my hair, losing weight and on the way out. I'm not. I'm as active as I've ever been. I really believe we will get through this."