Bladder Cancer in Dogs and Cats

TL;DR. Bladder cancer, particularly transitional cell carcinoma, is a serious condition in dogs and cats that causes urinary distress, blood in the urine, and potential blockages, requiring careful diagnosis and specialized treatment.

Bladder cancer can affect both dogs and cats, requiring careful veterinary evaluation.

What is it?

Bladder cancer refers to abnormal, uncontrolled cell growth within the urinary bladder. In both dogs and cats, the most common type of bladder cancer is transitional cell carcinoma (TCC), also known as urothelial carcinoma. This tumor originates in the transitional epithelial cells that line the inside of the urinary tract. These specialized cells are designed to stretch as the bladder fills with urine, but when they undergo malignant transformation, they form invasive tumors that compromise the bladder's structure and function.

These tumors most frequently develop in the bladder neck, an area known as the trigone, as well as the dorsal (upper) bladder wall. The trigone is a highly sensitive triangular region where the ureters (the tubes carrying urine from the kidneys) enter the bladder and the urethra (the tube carrying urine out of the body) exits. Because tumors commonly grow in this narrow junction, they pose a severe risk of physical obstruction, blocking the normal flow of urine.

As the tumor grows, it invades the deeper layers of the bladder wall, leading to chronic inflammation, bleeding, and discomfort. For pet owners, understanding this disease is critical because its early signs closely mimic routine urinary tract infections, often delaying a correct diagnosis until the tumor has reached an advanced stage.

Causes & risk factors

The exact cause of bladder cancer in dogs and cats is multifactorial, involving a mix of genetic predispositions and environmental influences. While any dog or cat can develop bladder tumors, certain breeds carry a significantly higher genetic risk.

Environmental factors, such as exposure to certain older-generation pesticides, herbicides, and topical flea control products, have historically been studied as potential risk factors in dogs. Chronic bladder inflammation from recurrent urinary tract infections or bladder stones may also play a role in damaging the bladder lining, potentially paving the way for cellular mutations. In cats, bladder cancer is overall less common than in dogs, but when it occurs, it behaves with similar invasiveness and requires the same prompt medical attention.

Signs to watch for

The clinical signs of bladder cancer are primarily related to irritation of the lower urinary tract and physical blockage of urine flow. Because these signs overlap heavily with common bladder infections (cystitis) and bladder stones (calculi), any persistent urinary issue should be thoroughly investigated.

Common Signs

• Straining to urinate (dysuria): Your pet may spend a long time in the urinating posture, producing only small drops of urine.
• Blood in the urine (hematuria): The urine may appear pink, red, or contain visible dark specks of blood due to the bleeding tumor surface.
• Urethral obstruction: The tumor physically blocks the exit of the bladder, preventing your pet from passing urine. This is a life-threatening emergency.

Occasional Signs

• Blood clots: Large clots can form in the bladder and pass in the urine, sometimes temporarily worsening blockages.
• Urinary tract stones (calculi): Stones can co-exist with the tumor, causing additional irritation.
• Bladder inflammation (cystitis) and urethral inflammation (urethritis): The tumor causes chronic, painful swelling of the local tissues.
• Fluid buildup in the ureters (hydroureter): If the tumor blocks the entry points of the ureters, urine backs up toward the kidneys, causing painful stretching of the tubes.
• Postrenal azotemia: A buildup of toxic waste products in the bloodstream because the kidneys cannot excrete them past the blockage.
• Electrolyte imbalances: Severe disruptions in blood minerals caused by kidney dysfunction.
• Hyperkalemia-induced life-threatening arrhythmias: When urine is blocked, potassium levels in the blood rise dangerously (hyperkalemia), which directly disrupts the heart's electrical rhythm, potentially causing sudden cardiac arrest.

Straining to urinate and blood in the urine are primary warning signs of bladder tumors.

How vets diagnose it

Diagnosing bladder cancer requires a systematic approach to differentiate the tumor from benign conditions like urinary tract infections or bladder stones. Your vet will begin with a physical examination, which may include gentle palpation of the abdomen to feel for a thickened bladder wall or a physical mass.

Ultrasonography

Abdominal ultrasound is an invaluable, non-invasive tool for visualizing the inside of the bladder. It allows the vet to see the location, size, and characteristics of the mass. A leading veterinary ultrasound textbook describes the typical appearance of these tumors:

"The echogenicity is often mixed and has an overall appearance that can be poorly to moderately echogenic. It may also be partly mineralized, which can be confused for calculi. The masses are described most commonly in the bladder neck (trigone) region and dorsal bladder wall... however, they can be seen at any location in the bladder."

Because the tumor can contain calcium deposits (mineralization), your vet must carefully distinguish it from actual bladder stones.

The Danger of Needle Biopsies

If a bladder mass is found, your vet will avoid performing a standard needle biopsy through the belly wall (percutaneous fine-needle aspiration). This is because TCC cells are highly prone to "tumor seeding"—sticking to the needle and transplanting themselves along the needle track, spreading the cancer to the abdominal wall. A standard veterinary internal medicine manual notes:

"Hence if a dog has a potentially resectable apical bladder mass, the author does not do percutaneous FNAs but rather transurethral, ultrasonography-guided catheter aspirates."

Advanced Diagnostic Tests

• Transurethral, ultrasonography-guided catheter aspirate: A safe technique where a catheter is passed through the urethra into the bladder under ultrasound guidance. Gentle suction is applied to collect tumor cells without puncturing the abdominal wall.
• Cystourethroscopy: A procedure where a tiny camera is passed into the urethra and bladder. This allows direct visualization of the tumor, catheter placement in difficult cases, and the collection of biopsy samples.
• Suction biopsy: Using a catheter to obtain larger tissue pieces for analysis.
• Histopathology [GOLD STANDARD]: The definitive diagnosis requires a pathologist to examine a tissue biopsy under a microscope. This confirms whether the mass is cancerous and identifies the specific tumor type.

Ultrasound is a critical, non-invasive tool used to identify bladder masses and monitor treatment.

Treatment options

Treatment for bladder cancer is tailored to the tumor's location, whether it has spread (metastasized), and the pet's overall health. Because these tumors are highly invasive, a combination of therapies is typically recommended.

Surgical Removal

Surgery is rarely a complete cure because most tumors are located in the trigone, where complete removal would destroy the bladder's connection to the urethra. However, if the tumor is located at the top (apex) of the bladder, surgery may be attempted. A prominent veterinary surgery reference outlines the precise technique required:

"If bladder neoplasia is suspected, the bladder wall is gently palpated and a cystotomy incision is made at least 2 cm away from the bladder mass. The mucosal surface of the bladder is inspected for additional tumors. The mass should not be manipulated during the cystectomy. The bladder wall with the mass is excised with a 1 to 2 cm margin of grossly normal tissue."

These strict guidelines help ensure that the surgeon does not accidentally spread cancer cells or leave tumor tissue behind.

Chemotherapy

Chemotherapy is the cornerstone of management for inoperable tumors. The COP Chemotherapy Protocol is a widely used combination protocol consisting of cyclophosphamide, vincristine, and prednisone. This protocol aims to shrink the tumor, slow its progression, and alleviate pain, helping to maintain a good quality of life.

Interventional Procedures and Monitoring

If the tumor is blocking the flow of urine, your vet may perform interventional procedures to keep the urinary tract open. This can include placing a urethral stent (a small metal mesh tube) or using cystourethroscopy to assist with catheter placement. A leading veterinary critical care manual notes that cystourethroscopy can also be used "for visualization during laser lithotripsy with the goal of breaking a stone into small enough fragments for extraction" if bladder stones are complicating the blockage.

Continuous monitoring is essential. As noted in a prominent ultrasound reference, ultrasound plays a key role in monitoring treatment response, though vets must remain vigilant, as "on rare occasions, seeding of TCC can be seen in adjacent tissues following" these interventional procedures, and intravesicular hemorrhage (bleeding inside the bladder) remains a potential complication.

Prognosis

Long-term prognosis data in this species is limited, particularly in cats, where the disease is less frequently documented. In dogs, transitional cell carcinoma is a progressive and serious disease. While a complete cure is rare, many pets can achieve several months to over a year of comfortable, high-quality life with a combination of chemotherapy, anti-inflammatory medications, and supportive care.

Without treatment, the prognosis is poor, primarily due to the high risk of complete urinary tract obstruction. Your vet will work closely with you to monitor your pet's comfort, appetite, and ability to urinate, adjusting the treatment plan to prioritize their quality of life.

Prevention

Because the exact triggers for bladder cancer are not fully understood, there is no guaranteed way to prevent it. However, you can minimize potential risk factors by:

• Avoiding the use of older-generation pesticides and herbicides in your yard.
• Ensuring your pet has constant access to fresh water to encourage frequent urination, which helps flush out potential carcinogens.
• Discussing routine screening, such as regular urinalysis or screening ultrasounds, if you own a high-risk breed.

When to call your vet

You should contact your vet immediately if you notice any changes in your pet's urination habits.

If your pet is straining and producing no urine, or if they appear weak, lethargic, and are vomiting, this is a life-threatening emergency. A complete urinary blockage can lead to fatal heart arrhythmias within 24 to 48 hours due to potassium buildup. Prompt veterinary intervention is required to relieve the obstruction and stabilize your pet's electrolytes.

For specific breeds

While bladder cancer can strike any dog or cat, certain breeds have a documented higher risk of developing transitional cell carcinoma:

• Cairn Terrier: This breed has a strong genetic predisposition to TCC, requiring close monitoring of any urinary symptoms.
• Labrador Retriever: Labrador Retrievers are also overrepresented in clinical cases of bladder neoplasia.
• Maine Coon: Among cats, the Maine Coon is noted for having an increased risk compared to other feline breeds.

If you own one of these breeds, pay extra attention to their urinary habits and consult your vet promptly at the first sign of straining or blood in the urine.

Sources

• Atlas of Small Animal Ultrasonography, 2nd Edition, pp. 385, 398
• Internal Medicine, 5th Edition, p. 1161
• Current Techniques in Small Animal Surgery, 5th Edition, p. 503
• Small Animal Critical Care Medicine, 2nd Edition, p. 788