COMPLETE REGRESSION OF TRANSMISSIBLE VENEREAL TUMOUR (TVT) IN NIGERIAN MONGREL DOGS WITH VINCRISTINE SULPHATE CHEMOTHERAPY

Intravenous administration of 0.025mg/kg body weight vincristine sulphate, in normal saline, in four weekly doses led to complete regression of lesions, within 35 days, in 4 mongrel dogs and 6 bitches with histologically diagnosed transmissible venereal tumour (TVT). Early side effects observed in the dogs, such as anorexia and dehydration disappeared after complete regression of the tumours. There was a progressive decrease in the number of mitotic figures, intercellular edema, bacterial contamination and inflammatory reaction within the tumour masses indicating that vincristine sulphate has direct effects on tumour cell division and bacterial multiplication. The tumour cells, initially very large (18-25μ; average 21.8±3.2μ diameter), with very abundant vacuolated cytoplasm and fine nuclear chromatin pattern, progressively became smaller cells (10-12μ; average 11.2±10.9μ) with heterochromatic nuclei and scant cytoplasm. Arrangement of tumour cells ranged from the initial glandular appearance to pallisading and compacted cells, which disappear as islands within thick fibrous connective tissue. Vascularization of the tumour masses also progressively waned. The presence of large numbers of lymphocytes, plasma cells and activated macrophages in the regressing tumours strongly suggests a role for immune-mediated control of TVT complimentary to that of vincristine sulphate. The slight and transient normocytic normochromic anaemia and leucopenia observed in the dogs may be related to the anti-mitotic effect of vincristine on bone marrow haemopoiesis. These untoward effects of vincristine may have been tolerated by the dogs because of the low dosage, short and well-spaced duration of therapy; an advantage over the adverse effects of some previously used combined anti-tumour drugs.

Keywords
Canine transmissible venereal tumour; progressive regression; vincristine sulphate, single chemotherapy