urinary bladder tumors

BACKGROUND

Bladder tumors are relatively common in dogs, but rare in cats. Some dog breeds, such as Scottish Terriers, are predisposed to bladder tumors. The vast majority of bladder tumors are malignant. The most common bladder tumor in both cats and dogs is the transitional cell carcinoma (TCC), but benign tumors (ie, papilloma and adenoma) and other malignant tumors (ie, squamous cell carcinoma, rhabdomyosarcoma, leiomyosarcoma, and hemangiosarcoma) have also been reported. Bladder tumors often produce clinical signs similar to urinary tract infections, such as hematuria (blood in the urine) and dysuria (urinary difficulties or straining), and hence diagnosis can be difficult.

DIAGNOSIS

Bladder tumors are diagnosed with urinalysis, blood tests, and imaging modalities such as contrast radiographs and ultrasound. A definitive diagnosis is possible with traumatic catheterization and urine sediment cytology. A cystoscope can also be used to collect biopsies, but this is not widely available. Ultrasound-guided fine-needle aspirates are not recommended because of the risk of seeding tumor cells into the abdomen, subcutaneous tissue, and skin.

CLINICAL STAGING

Chest radiographs or CT scans are done to check for metastasis to the lungs. An abdominal ultrasound is recommended to check for metastasis to the sublumbar lymph nodes and liver.

TREATMENT

Bladder tumors are difficult to treat because most TCCs are located in the trigone (where the ureters enter the bladder), most are advanced at the time of diagnosis (ie, they invade into the muscle layers of the bladder), and TCCs often involve the entire lining of the bladder (or urothelium). Based on criteria used in people, surgical removal of the entire bladder is recommended for muscle-invasive tumors. This is rarely performed in dogs because papers from the 1980s showed high complication rates and poor survival times. However, this is now being revisited by some surgeons with good results.

Currently, partial cystectomy in combination with chemotherapy is recommended for the treatment of TCC in dogs.

Urethral stenting or placement of a cystostomy tube is occasionally required for dogs with obstruction of urine outflow because of the tumor.

Chemotherapy is recommended and involves the use of non-steroidal anti-inflammatory drugs (ie, meloxicam, deracoxib or piroxicam) and mitoxantrone.

PROGNOSIS

The prognosis is fair to guarded for dogs with TCC of the urinary bladder. The median survival time for dogs with TCC treated with piroxicam alone is 181-195 days compared to 350 days for dogs treated with piroxicam and mitoxantrone.

To be updated