Common Types of Bladder Cancer in Dogs
The urinary tract of dogs is composed of the kidneys, ureters, urinary bladder, and urethra. Cancer can occur in any part of the urinary tract but it’s the urinary bladder that is most frequently affected. Bladder cancer comprises about 2% of all cancers in dogs. While bladder cancer can affect any dog, certain breeds appear to have higher risks of developing this type of cancer. Continue reading to learn more about the risks, symptoms, and treatment options for bladder cancer in dogs.
What is Bladder Cancer?
Several types of cancer can occur in the urinary bladder of dogs - transitional cell carcinoma (TCC), fibrosarcomas, leiomyosarcomas, and other types of soft tissue tumors.
Transitional Cell Carcinoma (TCC)
Transitional cell carcinoma (TCC) is the most common type of cancer of the urinary bladder of dogs. It’s also referred to as urothelial carcinoma. TCC is a highly invasive malignant tumor of the cells that line the urinary bladder. TCC can also affect the kidneys, ureters, urethra, prostate, or vagina of dogs. It can metastasize (spread) to other major organs of the body including the lungs, bones, liver, and lymph nodes.
As the tumor grows in size, it can obstruct the normal flow of urine from the kidneys to the urinary bladder or from the bladder during urination. Unlike most cases of bladder cancer in people which are low-grade and superficial, dogs often have the higher grade, invasive form that can grow and metastasize quickly throughout the body.
A dog that is unable to urinate is a medical emergency. Veterinary attention and intervention should be sought immediately.
Causes of Bladder Cancer in Dogs
The exact cause of TCC in dogs has not been fully established. Experts believe that several factors can increase a dog’s predisposition to TCC. These include genetics and environmental factors.
Dog breeds that are assumed to have a genetic predisposition because of the higher number of cases diagnosed include:
- Scottish Terriers
- Shetland Sheepdogs
- West Highland White Terriers
- Wire Hair Fox Terriers
Scottish Terriers have an 18-20-fold higher risk of TCC than other dogs. While Shetland Sheepdogs, Beagles, West Highland White Terriers, and Wire Hair Fox Terriers are 3 to 5 times more likely to develop TCC than other dogs.
Environmental factors that are suspected to play an important role in the development of TCC in dogs include exposure to certain types of pesticides and insecticides. Since smoking is the top cause of TCC in humans, studies are being performed to determine if second-hand smoke can also be an important risk factor in dogs.
Cases are also most common among middle-aged or elderly female dogs.
Symptoms of Bladder Cancer in Dogs
- Straining to urinate
- Frequent urination
- Painful urination
- Blood-tinged urine
These symptoms are usually also seen in dogs with urinary tract infections. Antibiotics will initially improve the symptoms, but if cancer or another issue is present, recurrence occurs within a short span of time.
How Bladder Cancer is Diagnosed in Dogs
More than 50% of dogs diagnosed with bladder cancer have TCC that involves the urethra. A tumor in the urethra can block urine flow, causing the affected pet to strain while attempting to urinate. If urine is unable to pass through, it can eventually lead to damage to the kidney and possibly kidney failure.
The tumor usually develops in the lower neck of the urinary bladder, which makes surgical removal impossible. This causes a partial or complete obstruction to the flow of urine during urination.
The tumor may be felt by a veterinarian through the abdomen wall if it’s already large. A digital rectal exam may also reveal tumors in the abdominal lymph nodes if metastasis has occurred. If the tumor has spread to the bones, lameness and/or bone pain can be observed.
After a thorough physical exam, your vet may recommend the following tests to confirm the initial findings:
Sometimes, the urine of dogs with TCC has cancer cells. However, urinalysis is unreliable when it comes to diagnosing bladder cancer because similar cells may appear during urinary tract infections.
2. Blood work
Most dogs with TCC have normal blood work except when kidney function is already affected. But the blood work results can serve as baseline data when evaluating the effect of treatment options.
3. Veterinary Bladder Tumor Antigen (VBTA) Test
This test checks the urine of dogs for bladder cancer. However, false positives have been recorded in dogs with bladder infections.
Bladder tumors are rarely seen on abdominal x-rays unless they have spread to the bones. Chest x-rays are useful in determining whether bladder cancer has spread to the lungs.
A cystogram may be helpful when the veterinarian suspects the spread of the tumor to the dog’s urethra. The procedure uses a special dye to make the tumor visible during x-rays.
Abdominal ultrasound can help in assessing the tumor size within the urinary bladder and the size of adjacent lymph nodes.
5. Tissue Biopsy
This is performed as a definitive test to diagnose TCC or other cancer of the urinary bladder. Cells may be collected via a surgical biopsy or a urinary catheter and examined microscopically.
Cystoscopy can be used in female dogs. The procedure involves inserting a camera into the bladder to visualize the tumor. Cystoscopy can also be used for tumor biopsy.
Tumor Staging for Bladder Cancer
Once TCC is confirmed, “tumor staging” will follow to assess the extent of the tumor.
Purpose of Tumor Staging
- Help determine the best treatment regimen that will be followed
- Provide important information about the prognosis
- Establish baseline data regarding the tumor measurements. This can help determine if certain treatments that will be successful.
Tumor staging is achieved with the help of x-rays (radiographs), ultrasound, and CT scans to see if there is metastasis to the lungs, abdomen, lymph nodes, and other organs. These procedures can also evaluate changes in the kidneys as a result of urine flow obstruction. The exact location and the size of the tumor within the bladder can also be determined.
Treatment Options for Bladder Cancer in Dogs
The treatment regimen will depend on the information gathered from the various tests and procedures that have been performed.
Excision of the tumor is only possible when it’s located away from the neck of the bladder and urethra. The presence of important structures prevents surgical excision in this area.
If surgical removal of the tumor is not possible, radiation therapy has been known to be successful at controlling the growth of the bladder tumor. The procedure, however, has its downsides and challenges. These include the following:
- Radiation can cause scarring and shrinking of bladder tissues.
- Irritation of surrounding organs
- The bladder, which is the primary target of radiation, changes shapes depending on the amount of urine in the bladder or when pressure is exerted on the bladder by adjacent organs.
Certain medications have been known to cause remission and cancer control in some dogs. These include piroxicam (a type of NSAID) and vinblastine (a chemotherapy drug).
Since dogs with TCC are very prone to developing cystitis (bacterial infection in the bladder), there may be a need for frequent urinalysis, urine culture, and antibiotic treatment.
If the flow of urine into and out of the bladder is obstructed, stents can be placed in the spot where the obstruction is located (ureters or urethra) to open up the passage and restore the urine flow. A cystotomy tube can also be placed to bypass a urethral obstruction and allow for proper emptying of the urinary bladder.
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