With a quick check on the net, I found this:

"Wayne never had a healthy life. He got one of his lung removed in 1963, had a heart surgery in 1978, and in the following year he had his stomach removed. John Wayne succumbed to cancer on 11 June 1979."

Of about 15 pages I visited, all said that he died of cancer, not a specific type. Usually, people of his age succumb to several different cancers, not just one. I know that he allowed the doctors to use him for experimental treatment - not to prolong his life, but to hopefully help future victims - he also helped to set up the John Wayne Cancer Inst. prior to his death.

pax yall