Cryotherapy is a method of killing cancer cells by freezing them. It is sometimes used to treat men with localised prostate cancer that has not spread beyond their prostate gland. Tiny probes called cryoneedles are inserted into the prostate gland through the wall of the rectum. They freeze the prostate gland and kill the cancer cells, but some normal cells also die. The aim is to kill cancer cells while causing as little damage as possible to healthy cells. The side effects of cryotherapy can include erectile dysfunction and incontinence. It is rare for cryotherapy to cause rectal problems or fistulas.