Page 667 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

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Tumors of the Urinary System

CHRISTOPHER M. FULKERSON AND DEBORAH W. KNAPP

Canine Urinary Bladder Tumors Etiology and Prevention

Urinary bladder cancer accounts for approximately 2% of all The etiology of canine bladder cancer is multifactorial. Risk fac-
reported malignancies in the dog. 1–3 With more than 65 million tors include exposure to older generation flea control products
dogs in the United States, and the estimated 6 million new canine and lawn chemicals, obesity, possibly cyclophosphamide expo-
cancer cases in the United States each year, even less frequent forms sure, female gender, and a very strong breed-associated risk (Table
of cancer, such as bladder cancer, affect tens of thousands of dogs 30.1). 1–3,13–15 The female-to-male ratio of dogs with TCC has
2,3
each year. Invasive urothelial carcinoma (iUC), also referred been reported to range from 1.71:1 to 1.95:1, although the sex
3
to as invasive transitional cell carcinoma, is the most common predilection is less pronounced in high-risk breeds. TCC risk is
form of canine urinary bladder cancer. 1–3 Most iUCs are inter- higher in neutered dogs than intact dogs of both genders, although
mediate- to high-grade papillary infiltrative tumors. 1–3 A series the reason for this has not been determined. 1–3,13
of 232 iUCs included 70% grade 3 (high grade) tumors, 29% In a case control study of 166 Scottish terriers (STs), TCC risk
grade 2 (intermediate grade) tumors, and 1% grade 1 (low grade) was significantly higher in STs that had been exposed to lawn her-
3
tumors. Other types of bladder tumors reported less frequently bicides and insecticides than in dogs not exposed, and the risk was
include squamous cell carcinoma, adenocarcinoma, undifferenti- significantly lower in dogs that ate vegetables at least three times
ated carcinoma, rhabdomyosarcoma, lymphoma, hemangiosar- per week in addition to their dog food. 14,16 The specific vegetable
coma, fibroma, and other mesenchymal tumors. 1–8 with the most benefit could not be determined, but carrots, given
iUC is most often located in the trigone region of the blad- as treats, were the most frequently fed vegetable. In contrast to
der. Papillary lesions and a thickened bladder wall (Fig. 30.1) are older types of flea dips, exposure to spot-on products containing
15
common features, and can lead to partial or complete urinary fipronil was not associated with an increased TCC risk. It would
tract obstruction. In a series of 102 dogs with iUC of the blad- appear appropriate to inform owners of dogs in high-risk breeds
der, the cancer also involved the urethra in 56% of dogs and
the prostate in 29% of male dogs. Nodal and distant metastases
1
were present in 16% and 14% of dogs, respectively, at diagno-
sis. Following World Health Organization (WHO) criteria for
1
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staging canine bladder tumors (Box 30.1), 78% of dogs had T
2
tumors and 20% had T tumors. In a necropsy study of 137
1
3
dogs with iUC, 58% of dogs had distant metastases and 42% *
had nodal metastases (including 33% of dogs with both nodal
3
and distant metastases). The lung was the most common site
of distant metastases (50% of dogs), with other sites including
liver, kidney, adrenal gland, spleen, bone, skin, heart, brain, and
3
gastrointestinal (GI) tract. At necropsy, second primary tumors
were noted in 13% of dogs, including hemangiosarcoma, lym- *
3
phoma, thyroid carcinoma, and others. Bone metastases were
reported in 17 (9%) of 188 canine iUC cases reviewed retro-
spectively, and in 3 (14%) of 21 dogs prospectively undergoing
total body computed tomography (CT) at euthanasia followed
by a standardized pathologic examination. In a series of 12
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dogs with cutaneous iUC metastases, gross lesions consisted of
plaques, papules, and nodules. iUC can occur in the abdomi- • Fig. 30.1 Dog, urinary bladder. Urothelial (transitional cell) carcinoma.
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nal wall, either through seeding from instruments and needles Transmural neoplastic growth involving the entire bladder (asterisk). One of
the iliac lymph nodes (black circle) is also infiltrated by this neoplasm. One
used in surgical and nonsurgical procedures, or through natural of the ureters is dilated (hydroureter, thin arrow) and the corresponding
spread of transmural lesions along bladder ligaments. iUC in kidney (opened, thick arrow) has hydronephrosis as a result of blockage of
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the abdominal wall is typically aggressive and poorly responsive the ureter at the trigone. (Courtesy J. A. Ramos-Vara, Purdue University.)
to medical therapy. 12
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