Radiation therapy and vaccine-associated sarcomas

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A retrospective study in Veterinary and Comparative Oncology examined both curative-intent and coarse fractionated radiation therapy in cats to determine efficacy in terms of survival times and progression free intervals. The authors identified 46 cats that had undergone curative-intent radiation, most of which had clean margins after surgery. They also identified 27 cats that had undergone a coarse fractionation protocol, most of which had dirty margins after surgery or macroscopic disease. One of the 46 cats that had curative treatment had concurrent chemotherapy. Thirteen of the 27 cats treated with the coarse fractionation also received  concurrent or subsequent chemotherapy.

The cats that received curative radiation therapy had a median survival time of 43 months and a median progression free interval of 37 months, with total doses of 45 or 48 Gy. This progression free interval is longer than previous studies that used even greater total doses of radiation. The survival and progression free interval had never been studied in cats undergoing coarse fractionated therapy for vaccine-associated sarcomas, and the results of this study were better than the authors expected-a median survival of 24 months and a median progression free interval of 10 months. These cats had received four fractions of 8 Gy once a week. They also found that coarse fractionated therapy was more successful in cats with no visible masses, that also received chemotherapy, and that had undergone fewer surgeries before radiation. The number of surgeries before curative-intent radiation and postsurgical histopathologic tumor margin results made no difference in the outcome. Another aspect of the study was to determine whether the Ki67 index, which has prognostic value in soft tissue sarcomas in people, holds value in cats. But this was found not to be prognostic for feline vaccine-associated sarcomas. The authors concluded that a combination of surgery and either curative-intent or coarse fractionated radiation therapy is an effective treatment option for cats with vaccine-associated sarcomas.

Eckstein C, Guscetti F, Roos M, et al. A retrospective analysis of radiation therapy for the treatment of feline vaccine-associated sarcoma. Vet Comp Oncol 2009;7(1):54-68.

Link to abstract: http://www3.interscience.wiley.com/journal/122201703/abstract