©1999 Good Dog! Magazine. All rights reserved. May not be reprinted or reposted without permission. www.gooddogmagazine.com
The Barking Edge of Medicine
by Rob Hilsenroth, DVM
© 1999 Good Dog! Magazine. All rights reserved. May not be reprinted or repostedwithout permission. www.gooddogmagazine.com
Cancer is a frightening word that conjures up images of weakness, nausea, hair loss, and death. In reality, cancer is a disease process where a cell continually divides and makes new cells, and doesn't respond to the body's normal signals to slow or stop its division. In benign tumors, the abnormal cells accumulate in one region and form a mass that doesn't spread to distant areas. Malignant tumors (cancer), on the other hand, invade the tissues where they originate and ultimately spread by a process called metastasis.
Dogs can develop many different kinds of tumors. Usually, cancer occurs in middle-aged to older dogs, but certain types of cancer also occur in younger dogs. Cancer of the urinary bladder occurs in dogs and cats. Transitional cell carcinoma is the most common tumor of the urinary tract in dogs, and tends to occur in older dogs, most often female, and more frequently in certain breeds such as Scotties and Shelties.
Dogs can develop several different types of bladder tumors, including cancer of the muscle wall and cancer of the inner lining cells of the bladder. Cancer of the lining cells, called transitional cell carcinoma, is the most common type of tumor of the urinary bladder in the dog. Transitional cell carcinomas are most often malignant tumors that can spread to others areas of the body, but also cause serious problems before they spread.
Envision the urinary bladder as a water balloon, with the neck of the bladder being equivalent to the area where one would fill the balloon or release the water. Transitional cell carcinomas usually grow in the area of the "neck" and make it difficult for patients to urinate, because the tumor obstructs the outflow from the bladder into the urethra and to the outside the body.
The symptoms owners notice in dogs with tumors of the urinary bladder resemble those seen in dogs with urinary tract infections. Fortunately, tumors of the urinary bladder are much less common than urinary tract infections. Dogs with bladder cancer will attempt to urinate frequently, but they may only produce small amounts of urine at each attempt, because the tumor may block the outflow tract. Dogs with infections of the urinary bladder also urinate frequently, because the bladder wall undergoes muscle spasms in response to irritation from bacteria. Dogs with bladder cancer may also have bloody urine due to leaky blood vessels in the tumor, and they may develop secondary infections.
As is true for many cancers, by the time owners recognize these signs, the tumor is often fairly large. In the advanced stages, bladder cancer may be acutely life-threatening, because the tumor can completely impede the dog's ability to urinate, or it can result in kidney dysfunction due to partial urinary obstruction.
Treatment of dogs with bladder cancer is difficult and, in the past, has rarely been successful. This is because the tumors are usually quite advanced by the time they're detected. It's usually not possible to surgically remove the entire tumor. Radiation therapy may be effective at killing the tumor cells, but it causes severe injury to the surrounding normal bladder tissues. The side effects of the radiation therapy can lead to clinical signs that are as bad -- or worse -- than those caused by the tumor itself.
When bladder tumors are identified at a very early stage, they can be treated using photodynamic therapy. Photodynamic therapy involves the use of compounds that make the tumor cells sensitive to intense light. The cells are then destroyed using laser light. However, photodynamic therapy is only effective when the tumors are very small, and there are very few places where this treatment is available. Various chemotherapy regimens have been tested to treat bladder cancer, but most have proven unsuccessful in prolonging life.
To improve the outcome of dogs with bladder cancer, Morris Animal Foundation is supporting the work of Dr. Deborah Knapp at Purdue University's School of Veterinary Medicine. Dr. Knapp is taking a new approach in the use of chemotherapy for dogs with transitional cell carcinomas of the urinary bladder. In the study entitled "Mechanisms of Synergistic Antitumor Activity of Piroxicam and Cisplatin in Canine Cancer," Dr. Knapp is evaluating a combination of two different drugs, piroxicam and cisplatin. Piroxicam is a non-steroidal anti-inflammatory drug that also appears to have antitumor effects against transitional cell carcinomas. Cisplatin is a chemotherapy drug that has had some activity against tumors of the urinary bladder.
Earlier studies have shown increased antitumor effects when these two drugs are combined against bladder cancer. Unfortunately, each of these compounds has inherent drawbacks and can be toxic even when used individually. Dr. Knapp and her colleagues are studying a treatment protocol combining these two drugs in order to determine if the tumors can be controlled or eradicated without harmful toxicity. If successful, this treatment could prolong the lives of dogs with bladder cancer while maintaining a good quality of life.
Rob Hilsenroth, DVM, is Executive Director of Morris Animal Foundation. This nonprofit organization sponsors animal health studies at veterinary schools and institutions throughout the U.S. and in other parts of the world. All annual unrestricted contributions to the foundation support health programs -- not the cost of administration or fund-raising.
If you'd like to make a contribution, write Morris Animal Foundation, 45 Inverness Drive East, Englewood CO 80112. For more information, call (800) 243-2345 or visit http://www.morrisanimalfoundation.org/.
©1999 Good Dog! Magazine. All rights reserved. May not be reprinted or reposted without permission. www.gooddogmagazine.com First published in Good Dog! July/August 1999.