Q: Taylor, my 9-year-old Sheltie, had what seemed to be a urinary tract infection, but the antibiotic prescribed for her wasn't completely effective. Eventually, her veterinarian diagnosed bladder cancer. What causes bladder cancer in dogs?
A: Transitional cell carcinoma, or TCC, is the most common form of bladder cancer in dogs. Transitional cells line the bladder, allowing it to stretch to hold urine while protecting the underlying layers from the urine's caustic effects. Because they line the bladder, transitional cells are exposed for a relatively long time to any environmental toxins excreted from the body.
So, it shouldn't be surprising that TCC most often targets dogs that live in industrialized areas or are exposed to herbicides or insecticides in the yard. Fortunately, oral and topical flea and tick products apparently do not increase risk.
TCC most commonly develops in middle-aged and older overweight female dogs. Certain breeds are predisposed—beagles, fox terriers, Scottish terriers, Shetland sheepdogs and West Highland white terriers—so genetics probably play a role.
Other risk factors are exposure to the chemotherapy drug cyclophosphamide and radiation therapy to the bladder.
Clinical signs are typical of a urinary tract infection: urinating small amounts frequently, straining to urinate and producing bloody urine. In dogs with TCC, these signs improve with antibiotics but don't resolve completely.
At the time of diagnosis, most dogs have a high-grade, invasive form of TCC in the trigone, the area of the bladder where the ureters from the kidneys enter and the urethra exits. Therefore, surgery is usually not a reasonable option.
Some nonsteroidal anti-inflammatory pain relievers extend survival time by four to six months. Standard chemotherapy drugs, radiation and laser therapy can further slow the progression of TCC and prolong survival.
Lee Pickett, V.M.D. practices companion animal medicine in North Carolina. Contact her at firstname.lastname@example.org.
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