Bladder tumors are the most common canine urinary tract cancer, accounting for about 0.5% of all neoplasia in dogs. While the majority of canine bladder tumors are transitional cell carcinomas (TCC), other carcinomas (adeno-, squamous cell, and undifferentiated), sarcomas, and even rare cases of lymphoma of the urinary bladder do occur. The median age of dogs with primary bladder tumors is 9.5 years or greater and they occur more frequently in females than in males.

Factors associated with the development of bladder tumors in dogs are: 1) a dose-related increase in incidence after application of topical flea control products (suspect chemicals include organophosphates, carbamates and/or pyrethroids, or the synergists/petroleum distillates they contain; 2) living in proximity to potential sources of agricultural/industrial toxins (marshy areas); and 3) obesity. It has been suggested that body fats acts as a reservoir for toxins resulting in a chronic low level exposure of the bladder epithelium to the carcinogens which induce these tumors. Also, since dogs have higher urine levels of tryptophan metabolites than other species, these compounds may contribute to the greater risk of bladder tumors in dogs. Acrolein, a metaholite of the chemotherapy drug, cyclophosphamide, is a well-known irritant that can produce sterile hemorrhagic cystitis, bladder fibrosis, and less commonly, TCC.

Any tumor that causes obstruction of the ureter, bladder trigone, or urethra may produce abdominal discomfort, vomiting, depression, loss of appetite, or azotemia. Invasion of the prostate can produce prostatomegaly. The majority of dogs with bladder tumors will present with the same non-specific clinical signs (hematuria, vaginal bleeding, strangurin and/or pollakiuria) that can occur with any urinary tract infection/inflammation, vaginal or prostatic infection/neoplasia, or urinary calculi. Many dogs with bladder tumors have a history of recurrent/persistent urinary tract bacterial infection despite otherwise "appropriate" antibiotic therapy.

Up to 30% of dogs with bladder tumors have a completely normal physical examination. Abnormalities, when detected, can include presence of a urethral or bladder neck mass by rectal or vaginal palpation, a caudal abdominal mass, prostatomegaly, outflow obstruction and bladder distension, abdominal pain, weakness, and sublumbar lymphadenomegaly. Respiratory signs, lameness, preputial edema, ascites, perineal hernia, and fever occur less commonly.

Obstruction of ureters or urinary outflow tract will result in azotemia. Non-specific elevations in serum alkaline phosphatase are found in 30% of dogs with bladder tumors, and serum alanine aminotransferase (ALT) is elevated in 20%. Twenty percent of dogs will have neutrophilia and 8% are anemic. Hematuria (even with urinary clots) along with an inflammatory urine sediment are consistent urinalysis findings. While cells that appear malignant are frequently found in the urine of dogs with bladder tumors, morphologically similar cells can be found in cases of urinary tract inflammation. A test for Bladder Tumor Associated Analytes (VBTA, Bion Diagnostic Sciences, Inc., Redmond, WA) has been developed for detection of the abnormal high-molecular-weight polypeptide complexes of basement membrane proteins present in the urine of dogs with TCC. The reported sensitivity of the test is 90% and the specificity is 78%. There is the potential for false positive results with 4+ proteinuria, 4+ glucosuria, or >30-40 red blood cells and/or white blood cells per microscopic high power field. Therefore, the results of this test must be considered in conjunction with history, clinical signs, and results of other preliminary diagnostics.

Initial survey radiographs may be unremarkable or may only demonstrate concurrent cystic calculi. Other radiographic abnormalities include pulmonary metastases (17%), suhlumbar lymphadenomegaly (9%), invasion of lumbar vertebrae or metastasis to bone (8%) or a caudal abdominal mass (6%). Double contrast cystourethrogaphy will identify masses or filling defects in up to 96% of cases. Due to increasing availability and practicality, ultrasonography is becoming the imaging method of choice for urinary tract disease. Where available, fiberoptic cystoscopy allows direct visualization of the urethra and bladder mucosa.

A definitive diagnosis of bladder cancer requires a biopsy for histopathologic evaluation. These can be collected by "traumatic catheterization", needle biopsy with ultrasound guidance, cystoscopically, or surgically.

Complete surgical excision of canine bladder tumors is the treatment of choice. Up to 80% of the apical portion of the bladder can be excised with recovery of adequate reservoir function. If the tumors are multifocal, diffuse, or involve ureters, the trigone or urethra, simple partial cystectomy will be inadequate. Selected cases have been treated with vaginourethrectomv, prostatectomy, transposition of the ureters to the colon, and/or transabdominal placement of cystotomy catheters with varying degrees of success. Due to the side effects of bladder fibrosis and incontinence, radiation therapy is generally considered to be an inappropriate choice for bladder tumors. Chemotherapy with intravesicular thiotepa or systemic cyclophosphamide, cisplatin, carboplatin, or combinations of anthracyclines (doxorubicin/mitoxantrone) with cyclophosphamide or platinum agents have yielded such inconsistent results that there is no “standard” chemotherapeutic approach. Piroxicam, a nonsteroidal anti-inflammatory drug (NSAID), has produced a response rate of 17% at a dose of 0.3 mg/kg/day orally. Although gastrointestinal irritation, nephrotoxicity (never combine with cisplatin), or decreased platelet function can be side effects of any NSAID, piroxicam has become the default drug of choice for treating bladder tumors due to its convenience, relatively low toxicity, and reasonable cost.

References: Knapp DW, et al, JVIM 8:273-278, 1994; Withrow SJ. In Withrow SJ, MacEwen EG (eds): Small Animal Clinical Oncology, Philadelphia, WB Saunders, 1996, pp. 385-390; Morrison WB. In Morrison WB (ed): Cancer in Dogs and Cats, Baltimore, Williams and Wilkins, 1998, pp..368-579; Rocha TA, et al, JVIM 14: 486-490. 2000.