Page 671 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 30 Tumors of the Urinary System 649

obstruction in a palliative setting or to maintain urine flow while Radiation Therapy
other therapies are instituted. 35–37 Complications can include Although iUC cells are generally thought to be sensitive to radia-
tion therapy (RT), an in vitro study of three canine iUC cell lines
urine leakage and tumor seeding, infection, tube displacement,
VetBooks.ir and tube damage if the dog is allowed to chew on the tube. revealed a low α/β ratio, suggesting moderate radioresistance and
supporting treatment protocols using higher doses and less frac-
46
Urethral and Ureteral Stent Placement and Laser Ablation tionation. The early use of large doses and less fractionation,
In recent years, the use of interventional radiology approaches has however, was associated with chronic colitis, cystitis, and urethral
gained favor over tube cystostomy and other surgical procedures strictures, and little improvement in MST compared with medical
for palliative management of obstruction secondary to iUC. 30,38–41 therapy alone. 47,48
Most urethral stents and some ureteral stents can be placed with With new advanced image-guided targeting technology and
minimally invasive approaches, and stents do not require pet own- increasing availability of RT, there is renewed interest in RT to treat
ers to manipulate a urine collection system. Survival after urethral iUC. 49–53 A retrospective report of intensity-modulated and image-
and ureteral stent placement is variable and largely dependent on guided radiation therapy revealed lower complication rates com-
49
the extent of tumor lesions. In three reports, MSTs have ranged pared with earlier studies in the dog. In a series of 21 dogs, acute
from 20 to 78 days (range, 2–536 days) after urethral stent place- side effects were mild and self-limiting and included colitis (38%),
ment for iUC or prostatic adenocarcinoma. 39–41 After urethral erythema or hyperpigmentation (19%), and stranguria (5%).
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stent placement, lower urinary tract signs, including stranguria, Late complications included urethral stricture (9%), ureteral stric-
can persist. Incontinence has been reported in 25% to 39% of ture (5%), or rectal stricture (5%). The median event-free survival
49
dogs. 39–41 Urethral stents are typically placed using fluoroscopic was 317 days and the overall MST was 654 days. In a report of 13
guidance, but the use of digital radiography to guide stent place- dogs with urogenital carcinomas treated with a low dose palliative
ment has also been reported. Ureteral stents can be placed sur- RT (10 daily fractions of 2.7 Gy with CT planning) plus antineo-
42
gically, and in some cases, nonsurgically in dogs with iUC. The plastic drugs, acute side effects were mild including colitis, cystitis,
50
MST after ureteral stent placement was 57 days (range, 7–337 vaginitis, and dermatitis, and no late complications were noted.
43
days) in one study. Nephrectomy can be considered for severe Complete remission (CR) or partial remission (PR) was reported in
unilateral hydronephrosis if persistent renal pain or infection is 61% of dogs and stable disease (SD) in 38% of dogs.
50
present.
Transurethral carbon dioxide (CO ) and near-infrared diode Medical Therapy
2
laser ablation of iUC (performed in combination with cytotoxic Systemic Medical Therapy
chemotherapy and COX inhibitors) has been reported, with its Systemic medical therapy is the mainstay of iUC treatment in dogs,
main application being in dogs with discrete tumor masses caus- and usually consists of chemotherapy, COX inhibitors (nonselective
ing urinary tract obstruction. 44,45 Complications include perfo- and COX-2 selective inhibitors), and combinations thereof (Table
ration with iUC spread, transient postprocedural worsening of 30.2). 1–3,27,54–62 Although medical therapy is not usually curative,
stranguria and hematuria, urethral stenosis, and infection. 44,45 In several different drugs lead to remission or SD of iUC, and most
a small series, the outcome of dogs treated with laser ablation and therapies are well tolerated. Resistance to one drug does not imply
44
medical therapy was not better than medical therapy alone. resistance to other drugs. Some of the best results are seen in dogs

TABLE 30.2 Study Results Reported for the Medical Therapy of Invasive Urothelial Carcinoma (iUC) in Dogs
Number of Dogs: N 1 or N 2 /M 1 /Any Median Survival
Total/Evaluable for Metastasis, (% of From Start of
Drug(s) Tumor Response Total Dogs) CR (%) PR (%) SD (%) PD (%) PFI (d) That Drug(s) Refs.

Randomized Trials
2 a
Vinblastine (2.5 mg/m ) 27/26 4/7/11 0 22 70 4 143 531 b 59
2
Vinblastine (2.5 mg/m )/ 24/24 0/4/4 0 58 33 8 199 299 59
piroxicam a
2 a
Cisplatin (60 mg/m ) 8/8 12/12/12 0 0 50 50 84 300 c 1–3
Cisplatin (60 mg/m )/ 14/14 28/14/43 14 57 28 0 124 246 1–3
2
piroxicam a,d
Cisplatin (60 mg/m ) 15 /14 20 /20 /33 0 13 53 27 87 338 e 62
2 a
Firocoxib (5 mg/kg) a 15/12 33/27/53 0 20 33 27 105 152 62
2
Cisplatin (60 mg/m /firo- 14/11 21/14/29 0 57 21 0 186 179 62
coxib (5 mg/kg) a
Mitoxantrone/piroxicam f 26/NA 8/NA/8 0 8 69 23 106 247 56
Carobplatin/piroxicam f 24/NA 29/NA/29 0 13 54 33 73 263 56
Continued