A retrospective study was conducted on the clinical cases of tumours in dogs brought to the Madras Veterinary College Teaching Hospital between September 2019 to May 2021. These included 629 cases of dogs with cutaneous or subcutaneous tumours. Mammary tumour constituted to 27.66% of all canine tumours (174 cases) as also reported earlier (
Johnson 1993;
Dorn et al., 1968 and
Moulton 1990).
The mean size of the tumours in Group I was found to be 3.70±0.94 cm and Group II 2.52±0.45 cm. All the tumours in the present study were non-ulcerated, round, freely movable and non-invasive solitary tumours. Absence of palpable enlargement of the lymph nodes was observed in the cases under study. There was no change in consistency of the lymph nodes (Table 1). According to
Misdorp (2002), metastasis to the regional lymph node was the earliest step in metastasis. Absence of distant metastasis was noticed on a lateral and ventro-dorsal thoracic radiography in all the 12 cases. Among the 12 cases, 2 cases in Group I were categorized under stage III because the tumour sizes were more than 5 centimetres. Three of the cases in Group I and 2 cases in Group II were categorized under stage II, since the tumour size was between 3 and 5 centimetres (Table 2). This clinical staging helped in providing a realistic prognosis to the owner. Bleomycin and cisplatin were chosen for the study since only these two drugs were identified as potential drugs for electrochemotherapy by
Mir (2006) and
Lowe et al., (2017). The cytotoxicity of cisplatin as observed by
Patrick et al., (1984) was due to direct binding to the DNA and inhibition of its synthesis and was proven to combat a variety of malignancies like sarcomas, cancers of soft tissues, bone, muscle and blood vessels observed by
Desoize and Madoulet (2002). The cytotoxicity of bleomycin was mainly due to direct DNA damage. The presence of injected drug in the target tissue determined the efficacy of electrochemotherapy. The electric pulses were applied using stainless steel plate electrodes in two perpendicular directions covering the entire surface of the tumour which was said to generate a transmembrane potential difference according to
Neumann et al., (1982). This transmembrane potential difference resulted in cell electroporation by generation of hydrophilic long-lived pores, according to
Weaver and Chizmadzhev (1996) and
Teissie et al., (2005). Bharathidasan et al., (2019) however opined that the uptake of drugs proceeded through an endo-cytic-like mechanism instead of electroporation.
The advantage noticed in the procedure was its short duration of time, simplicity and low dose of cytotoxic drugs with insignificant side effects and hospitalization was not required in any of the cases. There was an apparent decrease in the mean value of tumour volume in both the groups on the 30
th day when compared to day 0 (Table 3). This could possibly be attributed to the fact that electric pulsation increased the toxicity of bleomycin by several thousand folds and the fact that several hundred molecules of bleomycin inside the cell were sufficient to kill the cell
(Poddevin et al., 1991).
Cisplatin was less potent in electrochemotherapy possibly because there was only seventy fold potentiation when electric pulses were applied when compared to several thousand folds in bleomycin. Cisplatin on the other hand had higher potential in clinical practice due to its effectiveness in many chemotherapy protocols
(Sersa et al., 1995). Factors like survival time and disease-free interval have not been taken into the study like in the study by
Karayannopoulou et al., (2001) and hence the efficacy of electrochemotherapy for mammary tumour in long term remains uncertain. In group I, cases 1, 2, 3, 5 and case 6 from Group II showed fewer clusters of neoplastic cells when compared to the pre-chemotherapy cytology slide. (Table 4 and 5) All the other cases did not show any signs of malignancy. This could also be misinterpreted as stable disease since these add-up to the bulk of the tumour.
There were no intra-therapeutic complications observed during the except muscle twitching during application of electric pulses in all cases.The adverse effects following electrochemotherapy were recorded and graded as per Veterinary Cooperative Oncology Group-Common Terminology Criteria for Adverse Events (VCOG-CTCAE). Except for cases 1, 2 and 3 in Group I, all the other cases showed tumour necrosis as a local reaction to electrochemotherapy. According to
Snoj et al., (2005) and
Shimizu et al., (2003), electrochemotherapy was considered as a cyto-reductive technique before surgical resection.This was true with the current study where three dogs from Group I and one dog from Group II which partially responded to the therapy underwent a simple mastectomy to remove the cyto-reduced mass. Simple mastectomy was preferred since the tumour size had reduced considerably and
MacEwen et al., (1985) found no difference in recurrence rate and survival time between simple mastectomy and chain mastectomy. Reduction in tumour size was correlated to a better prognosis even after surgery according to
Vail et al., (1990) who found that smaller sized tumours had a better prognosis.Though surgery was considered as the best treatment for mammary tumours, high mortality was still observed by
Stratmann et al., (2008), proving that surgery alone might not be sufficient.
