Among the more investigated antineoplastic therapeutic options, the anti-angiogenic therapy has no important collateral effects for the patient. This therapy targets the factors implied in the progress of the angiogenic cascade, to impede the vascular support of tumoral tissue, increasing the apoptosis of the neoplastic cells.In this study the changes of the vascularization of canine venereal transmissible tumor (CTVT) were studied, both in the progressive phase of growth and during regression induced by treatment with vincristine sulphate (VCR). This antineoplastic drug apart from its cytostatic effect on tumors, it has demonstrated direct antivascular effect.Histopathologically with Papanicolau stain, was observed that after the treatment, the number of blood vessels diminished significantly (p