A hunting companion died last February. He went into the hospital with extreme pain in his leg, which they determined to be cancer. He had been in the hospital a year before with various ailments including blood pressure and heart, and they did not put it all together. They opened him for surgery and quickly realized that there was nothing that they could do, so they sewed him up, told his family the bad news, and referred him to hospice. He was dead within 4 days. The root cause was undiagnosed colon cancer that spread through his body and became impossible to miss when it got into his bones.
A strange story about injury from a colonoscopy:
A fellow I know in Atlanta went in for a scope. He had an unusually thin colon wall, and the doctor punctured it. He developed an infection, which manifested itself while the guy was on a cross country flight. He got so sick on the plane that it made an emergency, unscheduled landing in Phoenix (or Vegas or some other town short of Los Angeles) so that they could get him off. He spent days in the hospital far from home and his family had to travel there. Fortunately, he survived it.