I just finished reading Living Two Lives - Book 1. In telling the story of a childhood cancer patient it tells of the death by cancer of another child.
If we have a pet going through a painful death we are able to ease their pain and suffering with euthanasia. I could not make my dog suffer a painful death with cancer in his sinuses.
If we can do it for the pets we love why in the name of everything holy can we not do it for the people we love.