Page 197 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

176 PART III Therapeutic Modalities for the Cancer Patient

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A B

C D
• Fig. 11.1 Fluoroscopic images during a percutaneous ureteral stenting procedure in a 5-year-old male
castrated pit bull terrier. (A) An over-the-needle catheter has been placed in the renal pelvis and a contrast
nephroureterogram has been performed. (B) A guide wire is being passed down the ureter to the point of
the ureteral obstruction. (C) The guide wire can be seen extending through the ureter, through the bladder
and out the urethra in this male dog. (D) Final placement of the ureteral stent with a pigtail in the renal pelvis
and a pigtail in the bladder.

Intraarterial Chemotherapy
Whenever possible, surgical resection of gastrointestinal tumors
should be pursued. However, tumors occasionally grow unde- The use of intraarterial (IA) delivery of chemotherapy has long
tected in companion animals for extended periods of time, result- been considered in oncology. The proposed theoretical advan-
14
ing in large and/or invasive tumors that may be considered poor tages of IA drug delivery are that local drug concentration is
surgical candidates. Stenting of malignant obstructions in the gas- increased (i.e., at the level of the tumoral blood supply), tumor
trointestinal tract has been described for the esophagus and colon toxicity is not cell cycle specific because of high drug concentra-
in companion animals. 7,9,10 These procedures can be performed tions, and the decrease in systemic exposure to drugs leads to a
using a natural orifice; the author prefers to use a combination decrease in potential systemic side effects. 14,15 Several studies have
of endoscopic and fluoroscopic guidance during the procedure to demonstrated that IA infusion of drugs increases the concentra-
improve precision of stent placement. In a case report of a dog with tion of drug in the target organ. 16,17 In one study, IA drug delivery
an esophageal squamous cell carcinoma, stent placement resulted resulted in greater target organ concentrations of drugs compared
in an improvement in clinical signs for 12 weeks until euthanasia with intravenous (IV) administration. Studies have further
16
for unrelated reasons. Colonic stenting has been reported in two shown that drug concentration was influenced by blood flow rate,
9
cats and one dog. 7,10 All cases demonstrated clinical improvement i.e., vessels with a low arterial blood flow will have a higher local
after stenting. concentration of drug 16,18 ; however, many questions still remain
Stents have also been used to treat malignant obstruction of the about the magnitude of these proposed advantages (i.e., if these
trachea and extraluminal compression of blood vessels. A cat with advantages do exist, do they exist at a level that makes IA delivery
6,8
a tracheal carcinoma was evaluated for respiratory distress and noted a reasonable alternative to IV delivery?) and the pharmacologic
to have near complete obstruction of the tracheal lumen. Intralumi- activity of a drug in a higher concentration in the tumor.
nal tracheal stenting relieved the clinical signs and no complications The IA delivery of drugs comes with certain challenges, many
were noted. Endovascular stenting was used to relieve Budd– of which are magnified in a veterinary patient. Obtaining vascular
8
Chiari syndrome in three dogs with confirmed or suspected neo- access in an artery requires a small incision or ultrasound-guided
plastic obstructions. All three dogs demonstrated resolution of clini- intravascular access. When the artery used for access is not ligated
6
cal sings and extended survival times ranging from 7 to 20 months. but instead repaired, the access site needs to be monitored closely