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Urinary Tract Tumors

By Debbie Stoewen DVM, MSW, RSW, PhD; Christopher Pinard, DVM

Tumors, Pet Services

What is a urinary tract tumor?

A urinary tract tumor is a type of cancer that develops from the disorganized uncontrolled growth of cells that make up the urinary system. A tumor of the urinary tract could involve the kidneys, ureters (the tube that carries urine from the kidneys to the bladder), urinary bladder, prostate gland (in males), and urethra (the tube that carries urine from the bladder to the outside of the body).

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Bladder tumors are by far the most common type of urinary tract tumor. Of these, transitional cell carcinoma (TCC) is the most common. This type of tumor originates from the cells that line the bladder. Bladder tumors need to be distinguished from benign conditions such as inflammatory masses or polyps and noncancerous diseases that cause thickening of the bladder wall.

Primary kidney tumors are relatively rare in both cats and dogs and are almost always malignant. About 50% of these tumors arise from the cells that line the kidney tubules (passageways). These are called renal carcinomas. While renal carcinoma is the most common kidney cancer in dogs, renal lymphoma is the most common kidney cancer in cats.

Primary tumors of the urethra or ureter are also rare in cats and dogs. These types of tumors develop from the cells that line the ureter and urethra.

Tumors can also develop in the prostate gland in male dogs.

What causes this cancer?

The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary.

Urinary tract tumors are most common in middle-aged to older animals. However, a rare form of primary kidney cancer called a nephroblastoma usually occurs in dogs less than 1 year of age and young cats. Its cause is related to genetic changes that occur early in life. In German Shepherds, a mutation of a specific gene is associated with renal carcinoma and the development of a nodular skin condition called dermatofibrosis.

Bladder tumors in dogs have been linked to being overweight and to exposure to certain insecticides. It has also been proposed that chronic bladder infections and inflammation may increase the risk of developing bladder cancers. Certain breeds of dogs are more likely to develop bladder tumors, including the Scottish Terrier.

What are the signs of these types of tumors?

The signs of urinary tract tumors depend on what area of the urinary system is affected. Tumors of the ureters, bladder, and urethra can cause hematuria (blood in the urine), dysuria (straining to urinate), difficulty urinating, and frequent urination. Recurrent and often unresolving secondary urinary tract infections (e.g., bacterial cystitis) are commonly associated with these types of tumors. If the tumor obstructs the ureter, preventing the flow of urine to the bladder, the kidney will swell with urine causing signs of abdominal pain. If the tumor obstructs the urethra, there may be lethargy, vomiting, diarrhea, straining or the inability to urinate.

"The signs of urinary tract tumors depend on what area of the urinary system is affected."

Tumors of the kidneys can cause abdominal pain, blood in the urine, or non-specific signs such as lack of appetite, nausea or vomiting, weight loss, fever, lethargy, and swelling of the abdomen. Occasionally kidney tumors can cause increased urination and drinking.

Because many urinary tract tumors will spread (metastasize) to other areas in the body (including the bone), there may be signs elsewhere (such as lameness). Kidney pain can sometimes be difficult to distinguish from back pain.

How is this type of tumor diagnosed?

Your veterinarian may suspect a urinary tract tumor if your pet experiences recurrent urinary tract infections or the infections do not resolve with treatment. In this case, abdominal radiographs (X-rays) or ultrasound are usually recommended to determine the cause, such as an abnormal mass in the kidneys, bladder, or elsewhere along the urinary tract. With suspicion of any form of urinary tract tumor, your veterinarian will recommend bloodwork to assess kidney function and perform a urinalysis. Sometimes cancerous cells can be found in the urine.

"With suspicion of any form of urinary tract tumor, your veterinarian will recommend bloodwork to assess kidney function and perform a urinalysis."

Your veterinarian may find larger and/or firmer kidney(s) during a physical examination. In this case, usually abdominal radiographs or ultrasound are recommended, possibly with a tissue biopsy of the enlarged kidney. A biopsy is a surgical excision of one or more pieces of the abnormal tissue or tumor. This biopsy is then examined by a veterinary pathologist under the microscope. This is called histopathology. Histopathology is not only helpful to make a diagnosis but can indicate how the tumor is likely to behave. There are several kinds of biopsy techniques and your veterinarian or veterinary oncologist will recommend the best one for your pet.

Tissue samples of any bladder or urethral masses can be obtained by catheterization. This involves placing a urinary catheter into the urethra to retrieve potentially cancerous cells from the lining of the urethra or bladder. Another diagnostic option is cystoscopy, which involves passing a small scope (tube with camera) into the urethra and into the bladder to examine these areas, as well as obtain tissue biopsies for a pathologist to review. In dogs, there is a urine test for a specific mutation in the bladder cancer cells. This test may be recommended by your veterinarian or veterinary oncologist.

How do these types of tumors typically progress?

Benign tumors (especially of the kidneys) may be of no consequence, never causing any signs of disease. Malignant tumors, however, metastasize to other areas of the body, including the nearby lymph nodes, lungs, liver, bones, brain, spinal cord, and adrenal glands. Since tumors of the urinary tract are more likely to be malignant than benign, staging is always recommended prior to planning and starting treatment. Staging is the process by which diagnostic tests are performed to determine if (and where) the tumor has metastasized. Staging could include X-rays of the lungs, spine and hips to screen for spread to the lungs and bones. It may also include ultrasound of the abdomen to screen for spread to the liver, adrenal glands, and lymph nodes.

What are the treatments for this type of tumor?

The treatments for urinary tract tumors always depend on the type of tumor and degree of local invasion and metastasis. With bladder tumors, treatment is usually medical (e.g., NSAIDs) with or without chemotherapy and radiation therapy. As the area of the bladder most commonly affected is where the bladder connects to the urethra, surgery is not usually an option. It is only an option if the tumor is in another area of the bladder. With kidney tumors affecting only one kidney (and no evidence of spread), surgical removal of the kidney (nephrectomy) is usually the treatment of choice. With bilateral kidney tumors (tumors affecting both kidneys), chemotherapy may be considered, especially with renal lymphoma. In all cases of urine flow obstruction, immediate veterinary care is needed, as it is a life-threatening emergency.

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