He said he was clear of the disease.
http://www.dailymail.co.uk/tvshowbiz/article-3271494/Sir-John-Hurt-tells-joy-given-clear-pancreatic-cancerlooks-great-future.html
The doctors lied to him?
He acted with his voice and eyes, he never had muscles, never did stunts, he smoked and slowly pronounced meaningful lines (or just manuscritto craaap he made into smart lines by his ominous persona).