Preoperative radiotherapy for vaccine associated sarcoma in 92 cats

Medical records for 92 cats with a vaccine associated sarcoma receiving preoperative irradiation, with or without chemotherapy, between December 1985 and September 1998 were reviewed. The purposes were to quantify response to treatment and to attempt identification of factors associated with favorable response. Variables evaluated for a relationship to outcome included signalment, tumor location, presence of gross vs. microscopic tumor, radiation field size, irradiation technique, type of surgical procedure, completeness of excision, and chemotherapy (none, carboplatin alone, and others). Time to first event was calculated for the first day of treatment until local tumor recurrence or metastasis, or the date of euthanasia or death. Median time to first event for all 92 cats was 584 days. Only completeness of surgical excision was related to the time to first event. Median time to first event in cats having complete surgical excision was 986 days compared to 292 days for cats with incomplete excision (P = 0.004). Cats requiring bone removal to effect tumor removal had earlier failure than cats having other types of surgery. There was not a significant relationship between administration of chemotherapy or chemotherapy type and time to first event although outcome in cats receiving carboplatin was better than all other treatment groups. Carboplatin addition to preoperative irradiation appears worthy of further study. Preoperative irradiation is an effective treatment for cats with vaccine associated sarcoma, especially if complete excision can be accomplished following irradiation.