My husband is due to have surgery for rectal cancer on Thursday after having a cancerous polyp removed.. There is one question that is really distressing him. How does the surgeon know how much of a margin to take away round the cancer. He is petrified that they are going to take more than necessary away to be on the safe side and leave him with an ileostomy bag that he didn't perhaps really need. He is dead set against having a bag and is still thinking of calling the operation off because of this.