Experience of electrochemotherapy coupled with bleomycin in canine and feline oncology.

Electrochemotherapy (ECT) is a local ablative antitumour treatment that uses electric pulses to enhance the intracellular delivery of cytotoxic drugs. This treatment does not require multiple anaesthesia or high costs, and the side effects are minimal to none. ECT has been used in human and veterinary medicine for the treatment of cutaneous and subcutaneous tumours, but also for several other neoplasms. Therefore, new types of electrodes are constantly developed, clinical application is getting greater every day. This thesis discusses the retrospective evaluation of ECT in three tumour types in dogs and cats. The first study aimed to review the current treatment approaches for soft tissue sarcomas (STS) and evaluate the efficacy and safety of ECT. The study population of 52 dogs was arranged in three groups: (a) ECT alone, (b) intra-operative ECT and (c) adjuvant ECT. Recurrence rate (RR) and disease-free interval (DFI) were calculated. STSs were mostly located on limbs (77.8%). Median tumour size was 4.3 cm. Most STSs were grade I (47.7%) and II (50.0%), and histological margins were incomplete in 94.5% of cases. RR and DFI were similar between group b and c (23% and 25%, 81.5 and 243 days, respectively). Higher toxicity score was associated with higher pulse voltage (1200 vs 1000 V/cm) (P = 0.0473). Non-tonsillar squamous cell carcinoma (ntSCC) is a common and locally aggressive oral tumour in dogs, that is usually treated with surgery and radiotherapy. This second study included twelve dogs with ntSCC treated with ECT. Median tumour size was 1.65 cm, and the response rate was 90.9%. Overall RR was 27.3%. DFI and MST (median survival time) for dogs with recurrence were 50 and 115 days, respectively. All dogs with tumours smaller than 1-2 cm achieved complete remission without recurrence suggesting a favourable prognosis when using ECT. The third study dealt with feline nasal planum squamous cell carcinoma (npSCC) where surgery, radiation therapy and ECT are currently used as treatment modalities. This study included 61 cats treated with ECT. The aim was the evaluation of both, the efficacy and safety of ECT. The median tumour size was 1.5 cm. The overall response rate was 96.7%, RR was 22.5%, median DFI was 136 days, and median progression free survival was 65.5 days. Cats with toxicity >2 showed a higher probability of tumour recurrence/progression. Tumour-related death was higher in cats treated with 1 Hz (p = 0.035) and 1200 V/cm (p = 0.011) or 1300 V/cm (p = 0.016). Tumour size influenced local treatment response (p = 0.008) and toxicity (p < 0.001). Size was closely associated with treatment outcome (cut-off value for better response was <1.7 cm). Cats with tumours >1 cm, had a higher risk of a toxicity score of >2. In conclusion, local toxicity was mild in all three studies in half or more than half of the population and ECT has resulted safe and efficient for tumour local control and should be considered as an option for treatment of canine STSs, ntSCC, npSCC, and mast cell tumours, not only as a sole therapy but also combined with standard approaches. Future prospective studies on the influence of electrical parameters and treatment toxicity should be performed to better understand the results of the presented studies.