Cryosurgery is the use of a controlled stream of liquid nitrogen to freeze skin masses on the horse. This is a fairly non-invasive way to treat various skin cancers where surgical resection is difficult or dangerous. The horse is sedated and the area anesthetized with a local anesthetic. A small cone or shield is positioned over the mass and a concentrated spray of liquid nitrogen applied to the area. It is then allowed to thaw and the procedure repeated three times. As the mass freezes and thaws the water inside the tumor cell crystalizes and ruptures the cell, killing it. One specific advantage is that tumor tissue extending beyond the visible margin is also destroyed. Cryosurgery can also be used as an additional treatment combined with surgical debridement and local chemotherapy to treat squamous cell carcinoma, equine sarcoids, and mast cell tumors.