A retrospective study on cats with incompletely or marginally excised sarcomas treated with a bleomycin-only electrochemotherapy protocol: 66 cases

Introduction Electrochemotherapy (ECT) is a novel therapy used as an effective and safe treatment modality for both cats and dogs with various tumor types. This retrospective study aimed to evaluate the disease-free interval (DFI) for cats with incompletely excised or marginally excised sarcomas treated with a bleomycin-only ECT protocol. Methods A single institution retrospective evaluation was performed to identify cats as having undergone surgical removal of their sarcoma tumor followed by ECT from March 2015 to July 2024. In the absence of a standardized grading system for feline sarcomas, cats were stratified into high-grade and low-grade groups with primary emphasis on mitotic count. Median DFI was subsequently evaluated for each group. Results A total of 66 cats were identified and were divided into a high-grade group, which consisted of 43 cats treated with an average of 2 ECT treatments, and a low-grade group, which consisted of 23 cats treated with a single ECT treatment. Intravenous bleomycin was injected followed by a subcutaneous injection of bleomycin along the surgical scar in a 2:1 ratio. The surgical scar, as well as 2 cm of tissue surrounding the scar was then treated with electroporation with the following parameters: 8 biphasic waveforms; pulses duration of 100 μs; pulse repetition frequency of 1 Hz and pulse amplitude 1,200 volts/cm. Median DFI for the cats in the low-grade group was not reached whereas the median DFI for cats within the high-grade group was 389 days. This was statistically significant between the two groups. Conclusion This is the first study to evaluate a bleomycin-only ECT protocol in cats. Bleomycin-only ECT improved DFI compared to surgery alone for cats with incompletely or marginally excised sarcomas.