Most bladder tumors are transitional cell carcinomas
Some tumors are benign and are very treatable with surgery
Malignant tumors generally are treated with palliative measures:
- Urethra Stenting
- Cystostomy Tube
The urinary system is made of the kidneys, the tubes (ureters) that pass urine from the kidneys to the bladder, the bladder which is a reservoir for urine, and the urethra, which is the tube that drains urine from the bladder to the outside. The urethra in males is fairly long and a portion of it runs through the tissue of the penis. In dogs the penis has a bone (os penis) that surrounds the urethra for part of its length. The diameter of the urethra narrows as it passes through the os penis.
Bladder cancer is the most tumor of the urinary tract and comprises about 1% of all cancers in dogs and cats. Dogs develop this type of tumor more often than cats. Risk factors include nitrosamines, insecticide dips, cyclophosphamide, Sentinil, obesity, and living in an industrial location.
- average age is 10 years
- females develop the tumor more often than males
- breeds at risk: beagles, Scottish terriers, Shetland sheepdogs, Airedale terriers and collies
- average age is 9.7 years
- males develop the problem more than females
Behavior of the tumor
Bladder tumors are usually malaignant with only 3% of tumors being benign. Malignant tumors: transitional cell carcinoma is most commonly diagnosed, however other reported tumor types include squamous cell carcinoma, adenocarcinoma, fibrosarcoma, leiomyosarcoma and hemangiosarcoma, botryoid rhabdomyosarcoma. Benign tumors: fibromas, leiomyomas, and papillomas. Noncancerous growths: pyogranulomatous or polypoid cystitis. Most malignant bladder tumors invade the entire thickness of the bladder and diffusely involve the bladder at the time of diagnosis. At the time of initial presentation, about 50% of the patients have evidence of spread of the tumor to regional lymph nodes, pelvic and lumbar vertebrae and lungs; less commonly they spread to the liver and lymph nodes in the chest and abdomen (sternal and mesenteric nodes). At the time of autopsy, 75% of the patients have evidence of metastasis of bladder tumors.
In most cases, signs of a bladder tumor mimic signs seen with bladder infection and include bloody urine, incontinence, frequent urination, and straining to urinate. Inability to pass urine may becaused by obstruction of the urethra (tube that passes urine from the bladder to the outside) and this is considered an emergency.
Clinical signs of spread of the tumor to the back bones may include crying out in pain, reluctance to jump on elevated surfaces, sensitivity when the back is palpated and lameness/dysfuntion of hindlimb function (due to compression of nerves or spinal cord).
Clinical signs of advanced spread of the tumor to other parts of the body may include weight loss, loss of appetite, malaise, weakness, vomiting and breathing difficulties.
A mass in the bladder can be palpated by the veterinarian in only 12% of the cases, but those cases that have spread into the urethra can be diagnosed with digital rectal examation in 23% of the cases (for this reason it is critical for your veterinarian to always perform a digital rectal examination).
Routine blood work including a complete blood count and chemistry profile will not provide a diagnosis of a bladder tumor, however, is important to rule out tumor associated problems such as kidney compromise caused by obstruction ureters (tubes that pass urine from the kidneys to the bladder).
Testing of the urine should include urinalysis, cytology, and urine culture. Another test that can be run on the urine is the bladder tumor antigen test. If this test is negative, there is a very low chance that your pet has bladder cancer. If the test is positive, it does not mean that your pet has bladder cancer, as other disease such as urinary tract infection can give a positive test result.
Chest radiographs (x-rays) are made to rule out spread of tumor to the lungs. Radiographs of the pelvis may reveal spread of the tumor to the pelvic bones or lower spine; nuclear scintigraphy is a more sensitive test to evaluate for spread of cancer to the bones. Radiographs of the limbs are indicated if lameness is present and may show a condition called hypertrophic osteopathy; this condition causes the production of new bone to grow on the lower limb bones as a result of stimulation of the blood supply of the limbs by the bladder tumor.
Urinalysis frequently shows a concurrent bladder infection, but usually does not provide a diagnosis of the tumor
Fine needle aspiration of bladder tumors have been reported to cause spread of the tumor to the abdomen.
Traumatic catheterization technique can be used to collect cells from the tumor to help with making a diagnosis
The diagnosis of a bladder mass is usually based on ultrasound findings. In dogs, most transitional cell carcinomas will be located at the neck of the blader (trigone). In cats, however, this tumor tends to be located in the front of the bladder, but may grow in any region.
Cystoscopy is an excellent tool to help identify the extent and nature of the bladder tumor. Benign masses tend to be located in the front bottom (cranioventral) apsect of the bladder and usually are attached to the bladder by a narrow stalk (see video below right). Masses that are malignant tend to be located in the neck of the bladder. The video below left shows a small cancerous tumor of the bladder.
Treatment and prognosis
In years past, surgery has been recommended in most cases of bladder tumors. In one study that evaluated the effectiveness of surgery alone, the median survival time was 86 days. Surgeons have never been able to achieve clean surgical margins and tumor recurrence is expected in cases of transitional cell carcinoma. For this reason, tumors that are potentially benign, small tumors, and in a location that is easily treated will have surgery. Polyps that are large can be easily and successfully treated with surgery
Radiation therapy has extended life for about 1 year in about 61% of the patients. The side effects (colits etc) can be a major complication with radiation therapy.
The primary treatment for most bladder tumors includes treatment of the bladder infection with antibiotics, chemotherapy to try to stabilized the growth of the tumor or shrink the tumor and a nonsteroidal anti-inflammatory. In one study, Mitoxantron and doxorubicin demonstrated median survival time to 259 days. In two studies, cisplatin (a chemotherapy agent) resulted in a partial response in 39 to 79% of the dogs with median survival times of 130 to 180 days. A sister drug, carboplatin did not show any value for transitional cell carcioma in dogs. In another study, carboplatin and prioxicam resulted in median survival time of 161 days. Remission was achieved in 40% of the cases. Due to the toxic side effects seen in many animals, the investigators do not recommend this chemotherapy regimen for TCC. In another study CO2 laser ablation of the visible tumor and the entire lining of the bladder followed by treatment with mitoxantrone resulted in a median disease free interval of 200 days and median survival was 299 days. Although the survival times were similar to chemotherapy protocols alone, the period of time in which the patients had no signs of disease was significantly longer.
Prioxicam, a nonsteroidal anti-inflammatory mediation can provide relief of bladder pain by reducing inflammation and potentially an anti-tumor mechanism. In a study of 34 patients using this drug alone, 2 dogs had complete remission, 4 had partial remission and 18 had stabilization of the size of the tumor; the median survival was 181 days. Some oncologists will prescribe misoprostol when piroxicam is used to help prevent gastrointestinal ulcers and kidney damage.
Palliative stenting of the urethra (for dogs that have obstruction to urine flow due to tumor) resulted in good to excellent clincal function (no incontinence or urinary retention with ability to freely urinate in 3 of 4 females and 6 of 8 males. Unfortunately, the median survival time was only 20 days in this series of cases, but case selection may have influenced the outcome.
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