Transitional Cell Carcinoma (TCC) in Dogs and Cats

TL;DR. Transitional cell carcinoma (TCC) is a serious, invasive cancer of the urinary tract in dogs and cats that requires specialized diagnostics to prevent the accidental spread of tumor cells.

TCC most commonly develops in the trigone, the neck of the bladder where urine exits.

What is it?

Transitional cell carcinoma (TCC) is a highly malignant cancer that arises from the transitional epithelium—the specialized, stretchy layer of cells that lines the urinary tract. This lining allows the bladder and associated tubes to expand and contract as they hold and release urine. When these cells undergo malignant transformation, they form tumors that can aggressively invade the deeper layers of the urinary tract walls.

While TCC can technically develop anywhere along the urinary tract, it is most commonly found in the bladder neck (an area called the trigone), the dorsal (upper) bladder wall, or the urethra. Because of its location, the tumor often causes physical blockages, thickens the urethral walls, and interferes with normal urination. If left unchecked, the tumor can block the flow of urine from the kidneys to the bladder, leading to a dangerous backup of fluid.

One of the most distinctive and challenging characteristics of TCC is its tendency to "seed" or spread. If a needle is inserted directly through the abdominal wall into the tumor to collect a sample—a common procedure for other types of masses—cancer cells can cling to the needle and transplant themselves along the needle's path. This risk of tumor seeding makes TCC a disease that requires extreme care during the diagnostic process.

Causes & risk factors

Like most cancers, TCC does not have a single, identifiable cause. Instead, it develops due to a combination of genetic predispositions and environmental factors. Chronic irritation of the bladder lining may play a role in predisposing cells to abnormal changes. For example, the presence of bladder stones (urolithiasis) causes constant mechanical irritation to the delicate transitional epithelium.

Certain medical treatments can also induce changes in these cells. Exposure to specific chemotherapeutic agents, such as cyclophosphamide, is known to cause irritation and abnormal cell growth (hyperplasia with mild to moderate atypia) in the bladder lining, which can complicate diagnostics or potentially influence tumor development.

Genetics play a significant role, particularly in dogs. Certain breeds are statistically much more likely to develop TCC than the general pet population. In cats, TCC is far less common, but specific breeds still show a heightened risk.

Signs to watch for

The symptoms of TCC closely mimic those of a standard urinary tract infection (UTI) or bladder stones, which often leads to initial misdiagnoses. If your pet has urinary symptoms that do not resolve with standard antibiotic therapy, TCC should be considered.

Common Signs

• Blood in the urine (hematuria): This may appear as pink, red, or dark brown urine, and may occasionally contain visible blood clots.
• Straining to urinate (stranguria): Your pet may spend a long time trying to urinate, often producing only a few drops.
• Frequent urination (pollakiuria): Your pet may feel the constant urge to empty their bladder, leading to frequent trips outside or accidents in the house.
• Painful urination (dysuria): Your pet may vocalize, tense their abdomen, or show signs of discomfort while urinating.
• Leukocytes in urine: A high number of white blood cells in the urine sediment, indicating active inflammation.
• Atypical epithelial cells in urine: Abnormal cells shed from the bladder lining that can be detected during routine urinalysis.

Occasional Signs

• Hydroureter (unilateral or bilateral): If the tumor grows over the openings of the ureters (the tubes connecting the kidneys to the bladder), urine cannot drain from the kidneys. This causes the ureters and kidneys to swell with fluid, leading to kidney pain and potential kidney failure.

Rare Signs

• Tumor seeding in adjacent tissues: This typically occurs as a complication of invasive diagnostic procedures, where tumor cells are accidentally dragged into the abdominal wall or surrounding skin.

Straining to urinate is one of the most common signs of TCC, often mimicking a urinary tract infection.

How vets diagnose it

Diagnosing TCC requires a careful, step-by-step approach to confirm the presence of cancer while avoiding procedures that could spread the tumor cells.

Urinalysis and Cytology

Your vet will start by examining a urine sample. Under a microscope (urine sediment cytology or dry-mount sediment cytology), they will look for abnormal cells and inflammatory markers. However, a definitive diagnosis is rarely made from urine alone. As noted in a leading textbook on veterinary cytology:

"Urolithiasis and some chemotherapeutic agents (e. g. , cyclophosphamide) may induce epithelial hyperplasia with mild to moderate atypia... Variable numbers of epithelial cells and leukocytes are found in the urine sediment from animals with transitional cell carcinomas."

Because inflammation from infections or stones can make normal cells look abnormal (atypical), further testing is always required.

Ultrasonography

Abdominal ultrasound is the primary imaging tool used to visualize the bladder and urethra. TCC masses have a distinct appearance on an ultrasound screen. According to a prominent textbook on small animal ultrasound:

"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..."

If the tumor has invaded the urethra, the ultrasound may reveal "hypoechoic thickening of the urethral wall" and a highly reflective, bright line along the inner lining (a hyperechoic non-shadowing mucosal line).

Ultrasound is the primary tool vets use to identify bladder wall thickening and masses.

Tissue Sampling: The Crucial Precautions

To know for certain if a mass is TCC, a tissue sample is needed. However, because of the high risk of tumor seeding, your vet will avoid inserting a needle through the skin into the bladder (percutaneous fine-needle aspiration). A leading veterinary internal medicine reference states:

"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."

Instead of a needle, your vet will use safer, alternative methods to collect cells:

• Traumatic catheterization: A urinary catheter is passed into the bladder and gently manipulated against the tumor under ultrasound guidance to collect cell samples.
• Transurethral, ultrasonography-guided catheter aspirates: A specialized catheter technique to vacuum up tumor cells safely through the urethra.
• Suction biopsy or surgical biopsy: Obtaining larger tissue samples through specialized instruments or direct surgery.

Owners should note that catheter-based sampling carries a small risk of temporary bleeding inside the bladder (intravesicular hemorrhage).

Treatment options

The primary goals of treating TCC are to maintain your pet's ability to urinate comfortably, control pain, and slow the progression of the tumor.

Note: The structured veterinary record does not contain specific drug treatments or chemotherapy protocols for TCC. Your veterinarian or a veterinary oncologist will discuss the most current medical options available.

Surgical Options

Because TCC most commonly grows in the trigone (the neck of the bladder where urine exits), complete surgical removal is rarely possible. Removing this area would require reconstructing the entire urinary tract, which carries a very high rate of complications. However, if the tumor is located at the very top of the bladder (the apex), surgical removal of that portion of the bladder may be considered.

Medical Management

Veterinary oncologists typically manage TCC using a combination of medical therapies. These often include non-steroidal anti-inflammatory drugs (NSAIDs), which have been shown to have a direct anti-tumor effect against TCC in dogs, alongside various chemotherapy protocols.

Monitoring

Regular veterinary visits and ultrasound scans are essential to monitor how the tumor is responding to treatment. As noted in veterinary literature, "The monitoring of treatment response, especially in cancer patients, is useful" to determine if the current therapy is successfully holding the tumor at bay or if adjustments need to be made.

Prognosis

Long-term prognosis data in these species is limited in our primary records, and TCC is generally considered a progressive and challenging disease. Because it is highly invasive, complete cures are rare. However, many pets can maintain an excellent quality of life for months or even longer with appropriate medical management that controls inflammation, prevents secondary urinary tract infections, and keeps the pathway for urine open.

Without treatment, the tumor will eventually grow to completely block the urethra or ureters, which is life-threatening. Your vet will work closely with you to monitor your pet's comfort, appetite, and ability to urinate to ensure their quality of life remains high.

Prevention

There is no proven way to prevent transitional cell carcinoma in dogs or cats. Because the exact causes are multifactorial, prevention focuses primarily on early detection.

If you own a high-risk breed, talk to your veterinarian about proactive monitoring. This may include routine urinalysis starting around middle age to check for early signs of blood, white blood cells, or atypical epithelial cells, followed by screening ultrasounds if any abnormalities are detected.

When to call your vet

You should contact your veterinarian if you notice any changes in your pet's urination habits, especially if they have been previously treated for a urinary tract infection and the symptoms return.

Seek immediate emergency veterinary care if your pet:

• Is straining continuously and producing no urine at all (this indicates a complete urethral obstruction, which is a rapidly fatal emergency)
• Becomes extremely lethargic, begins vomiting, or refuses to eat
• Shows signs of severe abdominal pain or distress

For specific breeds

While TCC can affect any dog or cat, certain breeds have a documented genetic predisposition to developing this tumor:

• English Springer Spaniel: This breed has a higher statistical risk of developing bladder TCC compared to other medium-to-large dog breeds.
• Cairn Terrier: Cairn Terriers are among the small terrier breeds most frequently diagnosed with this disease.
• Maine Coon: While TCC is overall very rare in cats, the Maine Coon is one of the few feline breeds where a predisposition has been observed.

If you own one of these breeds, pay close attention to their urinary habits throughout their lives and report any changes to your vet immediately.

Sources

• Atlas of Small Animal Ultrasonography, pp. 385, 398
• Internal Medicine, p. 1161
• Diagnostic Cytology and Hematology of the Dog and Cat, p. 404