Chemotherapy plays a largely palliative role for solid tumors in veterinary patients. Most pet owners would not accept the complications encountered if their pets received the substantially higher doses of chemotherapy necessary to achieve the remission rates obtained in human patients. Intravenous (IV) chemotherapy doses used in veterinary patients are determined in order to achieve effective plasma levels without causing excessive morbidity; side effects from IV chemotherapy often result in dose-reductions which are less likely to achieve tumor control but will be better tolerated by the patient. Following an injection of IV chemotherapy, the drug flows centrally while being diluted by the other blood returning to the heart. Following dissemination via the arterial system, only a small proportion (and low concentration) of the drug will reach the actual tumor.
Alternatively, IR techniques permit fluoroscopically-guided, super-selective catheterization of the arteries feeding the actual tumor or body region. Intra-arterial (IA) administration of the systemic dose of chemotherapy permits significantly greater concentrations of the drug to reach the tumor without the systemic side effects that would be encountered had an equivalent IV dose been used to achieve the same local chemotherapy concentrations. Experimental studies in dogs and controlled studies in rabbits have documented the improved efficacy of these techniques in achieving higher local concentrations and improved tumor remission rates, respectively for certain types of tumors.30,31 These techniques have been used in veterinary patients for osteosarcoma32 and are currently being investigated in dogs with transitional cell tumors of the urinary bladder, urethra, and prostate.