Bladder cancer in dogs – symptoms, tests and treatment

Overview

The most common tumour often invades the bladder wall

Bladder tumours account for around 2% of malignant tumours in dogs. This describes the proportion of cancers, rather than every dog's disease risk. TCC is generally an aggressive tumour invading surrounding tissue. It is often located in the trigone, the triangular area at the bladder's base. Structures important for urine drainage lie close to this area.

The tumour can extend from the bladder into the urethra or prostate. It can metastasise, particularly to lymph nodes and lungs. Assessing local growth and metastases therefore affects treatment planning.

Not every bladder mass is cancer. An inflammatory polyp can resemble a tumour. The correct diagnosis guides treatment choice.

Causes

Tissue cells become malignant

Urothelial carcinoma can grow from the lining as a single or multiple papillary changes. It can also spread widely through the bladder and other urinary tract walls. Invasion of surrounding organs as well as the bladder wall is one possible progression pattern.

Some tumours have a BRAF gene mutation. This can be sought in cells shed into urine.

Disease risk involves both breed and environmental exposures. Previous cyclophosphamide treatment has been associated with bladder TCC. Associations do not mean every dog with the same exposure will develop disease.

Malignant change in the bladder lining can affect a wider area than one visible tumour. Metastatic tumours in the bladder are rare in dogs. Other malignant bladder tumours include adenocarcinoma and rhabdomyosarcoma, for example.

Risk factors

TCC occurs mainly in older dogs. In one case study, mean age at diagnosis was 11.05 years. Female sex and previous spaying or castration have been associated with increased risk. These are risk factors, rather than diagnoses.

Scottish Terriers have particularly high risk. Breed comparisons have described around 20 times the risk seen in crossbreeds. West Highland White Terriers, Shetland Sheepdogs and Beagles have been described as having 3–6 times the risk.

Obesity is one reported risk factor. Associations have also been found with some lawn chemicals and older insecticides. Exposure history therefore forms part of the overall assessment.

Typical symptoms

The most common observations involve urination. Possible signs include:

• Visible blood in urine.
• Painful-looking urination.
• Straining to pass urine.
• Needing to urinate more frequently.
• Greater tiredness than usual.
• Weight loss.
• Lameness.

Straining to defecate can also be a sign of lower urinary tract TCC. A bladder or urethral tumour can involve persistent bacterial infection. Signs may therefore reflect both a tumour and infection.

One-sided ureteral obstruction can cause abdominal pain. Obstruction on both sides or urethral obstruction can involve uraemic signs. Signs need investigation even if a previous antibiotic relieved some problems.

Complications and consequences

A local tumour can be serious even without metastases

Uncontrolled local growth can cause death through urinary obstruction. Ureteral obstruction can dilate the renal pelvis, causing hydronephrosis. Secondary urinary tract infections can be difficult to control.

Metastases present at diagnosis have been associated with a poorer outlook. Bone metastasis can underlie lameness. A bladder tumour can also spread into surrounding organs.

Medication can often control disease, although treatment generally does not cure the cancer. In some medication groups, median survival has been at least 1 year. Tumour grade and extent of spread affect the outlook.

In a study of radiotherapy-treated dogs with obstruction, 14 dogs, or 56%, developed acute radiation adverse effects. These affected the skin, gastrointestinal tract and bladder. Late urinary tract scarring and narrowing were suspected in 3 dogs, or 12%.

In a study of 102 dogs with bladder TCC, the urethra was involved in 56%. The prostate was involved in 29% of males in the study. At death, distant metastases have been reported in 49–58% of dogs with TCC.

Diagnosis at the vet

Samples and imaging complement each other

Investigations include physical examination, blood counts, blood biochemistry and urine tests. Rectal examination can detect thickening of the urethra or bladder base. Urine culture looks for concurrent bacterial infection.

Ultrasound and other imaging where needed establish tumour location and extent. Chest and abdominal imaging look for metastases. A lame dog may also have bone X-rays or CT. Staging helps distinguish local disease from disease that has spread elsewhere.

TNM staging describes the tumour's local extent and spread. At T2, it invades the bladder wall. At T3, it grows into neighbouring organs such as the prostate or vagina.

Urine cytology may show tumour cells. However, cytology can give both false negatives and false positives. An inflammatory bladder change can also resemble a mass without cancer.

Biopsy collection is planned carefully

Tumour tissue type can be confirmed with a biopsy taken endoscopically, through a catheter or during surgery. Endoscopy allows sampling of a visible change. A catheter sample's small size can reduce its diagnostic value.

Diagnostic accuracy of endoscopic biopsy has been reported as 96% in females and 65% in males with confirmed TCC.

Sampling through the abdominal wall can spread TCC cells along the needle tract or into the abdominal cavity. Because of this risk, urine may be collected by free catch or catheter rather than a needle into the bladder. Method selection therefore differs from that for an ordinary bacterial infection.

BRAF results depend on the testing situation

A urine BRAF test can support a urothelial carcinoma diagnosis. After a negative result, a suspicious tumour may need biopsy.

In Scottish Terriers entering screening without signs, an experimental BRAF test had a positive predictive value of 44%. The screening study's test also produced false positives and false negatives. This result concerns that particular screening test and dog population.

A tumour antigen test measuring basement membrane components is another urine test. It can also test positive with inflammation or blood in urine.

Treatment

Aiming for disease control and good quality of life

Medication is generally the mainstay of treatment. It may combine chemotherapy and cyclo-oxygenase-inhibiting NSAIDs. Your vet selects and monitors medication. Possible chemotherapy drugs include vinblastine and mitoxantrone, for example. Radiotherapy is an option for selected patients.

Surgery may be appropriate for obtaining tissue or restoring urine flow, for example. Removing the entire tumour is often difficult because of its location at the bladder base or in the urethra. The tumour can also recur or occur at several bladder sites.

In a study of 102 dogs undergoing partial cystectomy or tumour debulking, clear margins were achieved in only 2 dogs. Reducing tumour size and removing all cancer cells are therefore different treatment goals.

Tumour seeding onto the peritoneum has been found after surgery. In one comparison, it occurred in 18/177 dogs, or 10.2%, after cystotomy or cystectomy. Without these procedures, the proportion was 6/367, or 1.6%. Decisions therefore also consider procedural harm.

Urinary obstruction needs its own treatment

A stent, or expanding tube, can bypass urethral or ureteral obstruction. It keeps the urinary passage open but does not directly prevent tumour progression. Possible problems include incontinence, stent displacement, reobstruction and infections.

In one study, 15 of 25 radiotherapy-treated dogs with obstruction, or 60%, obtained relief. In the palliative radiotherapy group, median time to relief was 4 days, ranging from 2–7 days. In the group aiming for local tumour control, the median was 8 days, ranging from 2–10 days. Some dogs needed hospital care and a urinary catheter while waiting. A closed urinary passage must therefore not be monitored at home.

Of dogs obtaining relief in the radiotherapy study, 4, or 27%, developed another obstruction. Median time to reobstruction was 14 days from starting radiotherapy, ranging from 5–33 days. Two of these dogs later received a stent.

Treatment outcomes and monitoring

In a study of 76 dogs with TCC receiving piroxicam, median survival was 244 days.

In the piroxicam study, 2.6% of dogs achieved a complete response. A partial response occurred in 18.4%. Disease remained stable in 59.2%. It progressed during treatment in 19.7%. A complete response means examinations no longer detect the tumour.

With mitoxantrone and piroxicam combined, the reported median was 291 days. In dogs receiving radiotherapy for obstruction, median survival was 134 days, ranging from 6–969 days. These are outcomes from patient groups treated in different circumstances.

Response may be monitored every 4–8 weeks, for example. Medication is adjusted according to tumour response and treatment tolerability. Confirmed bacterial infections and urinary obstructions are treated at the same time.

Follow-up may include blood counts and blood biochemistry. Urinalysis and ultrasound tumour measurements complement monitoring. In an early cancer treatment study, metastases were sought using chest X-rays and abdominal ultrasound every 12 weeks.

Prevention

Breed background and environmental factors are associated with risk. Avoiding unnecessary lawn chemical and insecticide exposure is reasonable. The association particularly concerns some older insecticides. Your dog's parasite prevention is agreed according to their needs.

Early detection is different from preventing cancer. In a study, 120 symptom-free Scottish Terriers aged at least 6 years were monitored every 6 months for 3 years. Biopsy confirmed cancer in 32 dogs, or 27%. Monitoring allowed detection before urinary problems appeared. An appropriate investigation plan is assessed individually for an at-risk dog.

Important for dog owners

Urination and everyday wellbeing guide monitoring

Record whether your dog can urinate, blood in urine, appetite, movement and pain visible at rest. Difficulty urinating and blood in urine are common tumour signs. Establish with your treating vet whom to contact if the urine stream weakens.

Keep culture results and tumour measurements. Cancer-associated bacterial infection may need separate treatment. A new sign therefore does not always indicate tumour growth alone.

Report new urinary or abdominal signs during treatment. After stenting, issues monitored include incontinence and reobstruction. Also assess your dog's ability to sleep, eat and enjoy ordinary daily life. Treatment tolerability affects further treatment choice.

Frequently asked questions

Can bladder cancer look like a urinary tract infection?

Yes. Blood in urine, increased frequency and straining occur in many lower urinary tract diseases. A tumour can also involve persistent bacterial infection. Urine culture is therefore used as part of cancer investigation. Signs alone cannot identify a tumour and distinguish it from inflammation or infection.

Does a negative BRAF test exclude cancer?

No. If suspicion remains despite a negative genetic test, tumour biopsy may be needed. Urine cytology can also give false-negative results. Sample results are therefore combined with tumour imaging and your vet's other investigations.

Can the tumour always be removed surgically?

No. A location at the bladder base or in the urethra often makes complete removal difficult. Medication is therefore generally the mainstay of treatment. Surgery may still be used to obtain tissue to confirm diagnosis or secure normal urine flow.

Does a stent cure bladder cancer?

A stent aims to keep the urinary passage open. It does not directly alter tumour progression. A stent can involve incontinence, infections or another obstruction. A cancer treatment plan and monitoring of stent function are therefore needed alongside this procedure.

How long can a dog live with bladder cancer?

Survival depends on tumour grade, extent of spread and response to treatment. In the study of 76 dogs receiving piroxicam, the median was 244 days. In other medication groups, median survival has been at least 1 year. A median describes the group's midpoint, rather than an individual dog's deadline.