Everything You Wanted To Know About Bladder Cancer In Dogs
Bladder cancer comprises approximately 2% of all naturally occurring
cancers in dogs, similar to rates in humans. With more than 70 million pet dogs
in the United States and cancer developing in approximately 25% of older dogs,
it is expected that bladder cancer will newly affect more than 20,000
dogs each year.
Bladder cancer in dogs stages
The diagnosis is made by
histologic exam of tissue biopsies collected by surgery, cystoscopy, or
catheter biopsy. The vast majority of bladder cancer in dogs ( > 90%
of cases) consists of intermediate- to high-grade invasive Bladder Cancer.
Superficial, low-grade Bladder Cancer is very uncommon in dogs.
Bladder cancer in dogs risk factors
Risk factors for bladder
cancer in dogs include female sex, history of spaying or neutering,
obesity, breed-related severe risk, and exposure to older generation flea
control products and lawn chemicals. The female/male ratio of dogs with Bladder
Cancer has been reported to range from 1.71:1 to 1.95:1, with risk further
enhanced in spayed or neutered dogs. Vegetable consumption has been reported to
reduce the risk of Bladder Cancer in Scottish terriers with a substantial
breed-associated risk for the disease.
Bladder Cancer typically occurs in older dogs
with reported mean and median ages at diagnosis ranging from 9 to 11 years,
although the disease can occur much earlier in a minority of dogs. Bladder
Cancer is most often located in the trigone region of the bladder. Papillary
lesions and a thickened bladder wall can lead to partial or complete urinary
tract obstruction. Bladder Cancer has also been reported to involve the urethra
in 56% of dogs and the prostate in 29% of male dogs. Nodal and distant
metastases have been reported in approximately 16% of dogs at diagnosis and 50%
of dogs at death. When applying World Health Organization (WHO) criteria for
staging canine bladder tumours, 78% of dogs have been reported to have T2 tumours
and 20% of dogs have T3 tumours. There is a difference in the TNM staging
system between dogs and humans, with T2 tumours in dogs including muscle-invasive
disease, whereas muscle-invasive tumours in humans are classified as T3 or more
significant.
Bladder cancer in dogs
symptoms
Bladder cancer in dogs
symptoms included hematuria, pollakiuria, or dysuria. Less frequent clinical
signs included incontinence or polyuria and polydipsia. Out of 101 Bladder
cancer dogs, Six dogs (5%) had signs unrelated to bladder cancer and
were examined because of lameness due to bone metastases (4 dogs) or dyspnea
from pulmonary metastases (2 dogs). Bone metastases occurred to the lumbar
vertebrae and pelvis. The disease was discovered in nine dogs with bladder
cancer while another problem was being investigated. Owners observed signs
from 2 days to 52 weeks before admission to a veterinary hospital, with a
median time of 4 weeks. No physical abnormalities were detected in 35 dogs
(30%) with bladder cancer. In the remaining 80 dogs (70%), physical
abnormalities included urethral masses, either by rectal or vaginal
examination; palpable abdominal masses; prostatomegaly; distended bladders; or
evidence of abdominal pain. Neutrophilia was the most common abnormality
detected (20%). Anaemia was less frequently seen (8%) in dogs with bladder
cancer. Biochemical abnormalities included increases in liver enzyme activity
(45%), azotemia (13%), and hypercalcemia (5%). Two additional dogs with bladder
cancer had chronic renal failure, and two dogs with bladder cancer
had a post-renal obstruction. Urinalysis results were abnormal in 92 dogs (93%)
with bladder cancer, with hematuria, pyuria, proteinuria, and
bacteriuria most frequently noted. The method of urine collection was not specified.
Twenty-nine dogs (30%) with bladder cancer detected malignant cells in
the urinalysis. A fine needle aspirate of a bladder cancer palpable
abdominal/periurethral mass or a prostatic/urethral wash was diagnostic in 20 of
22 dogs (9 1%) and 10 of 13 (77%) dogs in which it was completed, respectively.
Ten dogs with bladder cancer had paraneoplastic diseases. Five dogs with
bladder cancer had hypercalcemia, three dogs had cachexia, one dog had hyperestrogenism,
and one dog had hypertrophic osteopathy.
Bladder cancer in dogs treatment
The treatment of bladder
cancer in dogs can include surgery, radiation therapy, chemotherapy and
other drugs, or combinations of these, although surgery and radiation therapy
are used less often than drug therapy in dogs. Complete cystectomy, the
front-line treatment for organ-confined invasive bladder cancer in
humans, is not typically performed in pet dogs because of the frequent presence
of cancer beyond the bladder (urethra, prostate, other organs), the morbidity
of the procedure, and the expense involved. Most bladder cancer lesions
in dogs are not in a location where complete surgical excision is possible.
Initial reports of radiation therapy in dogs with bladder cancer were
discouraging because of the side effects of the treatment. In recent reports,
however, newer radiation therapy approaches have been much better tolerated,
allowing further study.
Chemotherapy,
cyclooxygenase inhibitors, and combinations of these are dogs' mainstay of
treatment for primary and metastatic bladder cancer. Remission rates are
typically less than 20% with single-agent therapy and 35–50% with combined
chemotherapy and cox inhibitor treatment. Platinum agents appear to be the most
active in bladder cancer in dogs, especially when combined with a cox
inhibitor. Chemotherapy can be delivered to dogs with minimal risk of
bothersome side effects and with maintained or improved quality of life. Other essential
components of the care of dogs with bladder cancer include the placement
of urethral and ureteral stents when needed to relieve urinary obstruction and
aggressively treat the increasingly resistant secondary bacterial infections.
Although bladder cancer is not usually curable in dogs with current
therapies, the disease can be controlled in 75% of dogs, and the dogs can enjoy
many months to a year or more of good-quality life after diagnosis. The most
consistent prognostic factor is the tumor node metastasis stage, with the more
advanced stage associated with shorter survival. Across dogs with all stages of
bladder cancer, median survival times are typically between 130 and 195
days after single-agent drug treatment and more than 250 days after combination
drug treatments. When multiple treatments are given sequentially, survival can
extend well beyond a year. Thus, even though bladder cancer is rarely
curable, it is considered highly treatable.
Treatment studies in dogs
are expected to be a win–win–win scenario. The individual dog receives
treatment that is expected to help them and that often provides hope when other
treatments are not practical or not feasible. The results are expected to help
other dogs. Moreover, the results are expected to help humans with bladder
cancer ultimately. Many treatment trials for pet dogs also include funding
from the trial sponsor, which enables pet owners to pursue treatment for their
dogs even if they cannot afford other therapies. Most pet owners will also
allow a necropsy of the dog when it dies or is euthanized (because of declining
quality of life from cancer progression or other conditions). This provides
crucial information on the disease process and response to therapy and the
opportunity to bank tissue samples for future studies. Although most treatments
tested in dogs have been systemic therapies, dog studies can also be used to
evaluate intravesical therapy.
Bladder cancer in dogs prognosis
The prognosis for
dogs with bladder cancer is guarded, partly due to advanced disease at
the time of diagnosis. Late diagnosis of cancer in these dogs is commonplace
because the clinical manifestations of bladder cancer (eg, dysuria,
hematuria) mimic those of other lower urinary tract diseases. Late diagnosis
manifests itself clinically as the neoplastic disease that is not confined to
the urinary bladder or, in dogs with bladder-confined disease, primary tumours
that are not amenable to complete (curative) surgical resection
Bladder cancer in dogs survival rate
Dogs with bladder cancer had higher metastasis rates
at diagnosis have shorter survival rates. Primary bladder cancer localization,
sternal lymphadenomegaly and bone metastasis were identified as significant
variables individually associated with survival rates. Although
abdominal ultrasonography can provide valuable information in the
characterization of bladder cancers, whole-body CT may allow for a
thorough screening of the patient, leading to the detection of prognostic
findings such as intrapelvic bladder location, lymph node metastasis and bone
metastasis. In short, dogs having metastasized bladder cancer have a short
survival rate.
Bladder cancer in dogs when euthanized
The veterinarian recommends euthanasia due to poor quality of
life resulting from cancer or other conditions.
