Combination therapy using intratumoral bacillus Calmette-Guerin (BCG) and vincristine in dogs with transmissible venereal tumours: therapeutic efficacy and histological changes.

Therapeutic efficacy and histological changes after bacillus Calmette-Guerin (BCG), vincristine and BCG/vincristine combination therapy of canine transmissible venereal tumours (CTVT) were studied. Twenty dogs with naturally occurring CTVT in the progression stage were divided into 4 groups and treated with intratumoral BCG, vincristine, BCG/vincristine combination therapy or intratumoral buffered saline (control group). Tumour sizes were determined weekly and tumour response to therapy was assessed. Tumour biopsies were taken weekly to evaluate histological changes. Complete tumour regression was observed in all the dogs treated with BCG, vincristine and BCG/vincristine combination therapy. BCG/vincristine combination therapy had a statistically significantly shorter regression time than BCG or vincristine therapy. No tumour regression was observed in the control group. Intratumoral BCG treatment resulted in the appearance of macrophages and increased numbers of tumour infiltrating lymphocytes (TILs) followed by tumour cell apoptosis and necrosis. Treatment with vincristine resulted in increased tumour cell apoptosis, reduction in the mitotic index and a decrease in the number of TILs. Tumours from dogs on BCG/vincristine combination were characterised by reduction in the mitotic index, and appearance of numerous TILs and macrophages followed by marked tumour cell apoptosis and necrosis. This study indicates that combined BCG and vincristine therapy is more effective than vincristine in treating CTVT, suggesting that the clinical course of this disease may be altered by immunochemotherapy.