Effects of Electrochemotherapy with Cisplatin and Peritumoral IL-12 Gene Electrotransfer on Canine Mast Cell Tumors: a Histopathologic and Immunohistochemical Study

BACKGROUND: The study was aimed to characterize tumor response after combined treatment employing electrochemotherapy with IL-12 gene electrotransfer in dogs with spontaneous mast cell tumors (MCT). MATERIALS AND METHODS: Eleven dogs with eleven MCT(s) were included in the study. Histological changes were investigated in biopsy specimens collected before the treatment (T(0)), and 4 (T(1)) and 8 weeks (T(2)) later. Cellular infiltrates were characterized immunohistochemically by using anti CD3, CD20, Foxp3 (Treg), CD68 and anti MHC-class II antibodies. Proliferation and anti-apoptotic activity of neoplastic cells were assessed using anti Ki-67 and Bcl-2 antibodies. Angiogenetic processes were investigated immunohistochemically by using anti Factor VIII and anti CD31 antibodies and micro vessel density quantification. RESULTS: Histopathological examination of samples at T(0) confirmed the diagnosis and the presence of scanty infiltrates consisted mainly of T-lymphocytes and macrophages. At T(1) and T(2) neoplastic cells were drastically reduced in 7/11 cases, small clusters of neoplastic cells were detected in 3/11 cases and 1/11 cases neoplastic cells were still evident. Proliferation activity of neoplastic cells was significantly reduced at T(1) and T(2) and expression of anti-apoptotic protein at T(1). Microvessel density was drastically reduced in all samples after treatment. The number of T-lymphocytes increased at T(1), although not significant, while Treg were significant higher at T(1) and macrophages at T(2). CONCLUSIONS: The combined electrochemotherapy and IL-12 gene electrotransfer effectively induced a cellular response against neoplastic cells characterized mainly by the recruitment of T-lymphocytes and macrophages and a fibrotic proliferation with reduction of microvessels.