Canine Bladder Cancer
Cancer of the urinary tract in dogs can affect the kidneys, ureters, urinary bladder, prostate, or urethra. In the urinary system, the bladder is affected with cancer most commonly. Compared to cancer in other locations in the body, bladder cancer is unusual, comprising 1-2% of all cancers in the dog.
The most common cancer of the dog urinary bladder is invasive transitional cell carcinoma (TCC) of intermediate to high grade. TCC is a malignant tumor that develops from the transitional epithelial cells that line the bladder. In dogs, this tumor invades into the deeper layers of the bladder wall including the bladder muscles. Canine TCC also has the ability to spread to lymph nodes and to other organs in the body (lung, liver, and other sites). TCC most frequently is found in the bladder, but can also develop in the kidneys, ureters, prostate, and urethra. It can also spread from the bladder into neighboring organs. As a side note: 80% of humans with bladder cancer have a lower grade, less invasive form of TCC, but dogs and cats rarely get this less aggressive form of the cancer.
The exact cause of TCC in an individual dog is usually not known. In general, canine TCC results from a combination of several factors including genetic predisposition and environmental factors. A genetic predisposition is suspected because TCC is more common in specific breeds of dogs, including Scottish Terriers (18 fold increased risk compared to other breeds), Shetland Sheepdogs (4 fold increased risk), Beagles (4 fold increased risk), West Highland White Terriers (3 fold increased risk), and Wire Hair Fox Terriers (3 fold increased risk). Environmental factors identified as risk factors in previous studies have included pesticides, insecticides, and certain dietary factors. The greatest cause of TCC in humans is smoking, but further study is needed to determine the extent to which second-hand smoke may contribute to TCC in dogs.
Blood in the urine and straining to urinate are the most frequent signs of TCC. Pet owners must realize, however, that a urinary tract infection will cause these same symptoms, so the symptoms alone do not necessarily mean their dog has TCC. Less commonly, dogs with TCC can have lameness due to the spread of the tumor into the bones or coughing due to spread into the lungs. To diagnose TCC requires a tissue biopsy. Several other types of growths in the bladder, bladder infection, bladder stones, or bladder inflammation can cause similar symptoms as those in dogs with TCC. Some of these other conditions can cause abnormal cells in the urine, which can be mistaken for TCC. Therefore, diagnosis of TCC requires a tissue biopsy. A tissue biopsy can be obtained by surgery, cystoscopy (insertion of a fiberoptic scope into the bladder and biopsy through the scope), or in some cases with a urinary catheter.
Once a diagnosis of TCC is made, it is important to determine the extent of the tumor, i.e. to perform “tumor staging”. Tumor staging is performed to determine the best way to treat the cancer, to provide some information regarding prognosis, and to establish a baseline tumor measurement in order to determine if treatment is successful. Tumor staging for TCC includes radiographs of the thorax to look for lung metastasis, radiographs and ultrasound of the abdomen to look for metastasis in the abdomen and to assess any changes in the kidneys that result from obstructed urine flow. This information is needed to best plan how to treat the cancer. Also, these tests can be repeated during treatment to know if the treatment is being effective. Approximately 20-30% of dogs have metastasis to “distant” sites such as the lungs, but up to ½ will have “regional” metastasis to the surgical site and nearby lymph nodes.
For dogs with TCC that has not spread beyond the bladder, surgical excision is recommended. In order to surgically excise the tumor, however, it needs to be located away from the neck of the bladder and the urethra. Several vital structures in the neck of the bladder (where these tumors commonly develop) make surgical excision in this location usually difficult, but multiple studies have found that even removing just part of the mass is beneficial for an improved outcome. It is not possible to remove a “margin” of normal tissue around these tumors, except in rare cases, thus microscopic tumor cells are left behind post-op and lead to cancer regrowth.
The vast majority of TCC cases are treated with medical therapy using two drugs: chemotherapy and non-steroidal anti-inflammatories (NSAIDs). Traditional chemotherapy agents include Mitoxantrone, Carboplatin, Adriamycin, Vinblastine, and others have been used in canine TCC. The response with chemotherapy alone has been rather disappointing with ~20% of dogs having remission. NSAIDs are also effective in ~20% of dogs, but combining chemotherapy with an NSAID will yield response rates of 40-50%. Commonly used NSAIDs include Deramaxx, Piroxicam, Metacam, and Rimadyl. The side effects of chemotherapy are usually tolerable in dogs. Information of specific medications can be discussed with the attending veterinarian.
It is not known how long dogs with TCC that are not treated will live. Survival is affected by the growth rate of the tumor, the exact location of the tumor within the bladder, and whether the tumor has spread to other organs or not. The median survival in dogs treated with chemotherapy or NSAIDs alone is 3-4 months. The median survival time improves to 6-8 months when these therapies are combined. The best prognosis occurs for dogs that have medical therapy following surgery. In patients where minimal tumor remains post-op and they are followed with chemo and NSAIDs, the median survival time increases to 1-1.5 years. If bulky tumor remains post-op, the median survival time is 10-12 months if the patients are followed with chemo and NSAIDs.
Dogs with TCC are very prone to developing a bacterial infection in the bladder. Therefore, frequent urinalysis, culture, and treatment with antibiotics may be necessary. A secondary bacterial infection can result in a sudden worsening in symptoms in dogs with TCC, and these dogs will improve with treatment with antibiotics.