Sarcomas are malignant cancers of connective tissues. They can be movable lumps under the skin or growths that deeply attach to underlying structures. The incidence of these tumors has risen significantly since 1991, and vaccines (especially rabies and feline leukemia) appear to be associated with this increase. Complete removal of these tumors is nearly impossible since they are poorly defined and spread easily. Even in combination with radiation, the cure rate is low. Chemotherapy may be the one remaining option. Ifosfamide is one of the few chemotherapy agents that have proven effective in humans and dogs. These investigators will determine the appropriate clinical dose of ifosfamide in cats, define the toxic effects, and document the evidence of anti-tumor activity when used to treat cats with spontaneously occurring sarcomas. If successful, this could make a major difference in the treatment of cats with vaccination site sarcomas while increasing their survival rates.