How can I know for certain?

Over the past year or so I have visited with a man who was battling stage four cancer in three different organs. At times he was making good progress and was hopeful with chemo and surgery. However, while cancer in one area responded to treatment other areas of cancer did not. Finally, the decision was made after available treatments were exhausted to simply quit all treatment and let the cancer take its course. This is a scenario we hear of all too often.