58Â° Congresso Nazionale SCIVAC: Oncologia veterinaria

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58° Congresso Nazionale SCIVAC • Milano, 7-9 Marzo 2008 • Oncologia veterinaria - Alle soglie del III Millennio Bladder tumors comprise approximately 1% of all canine malignancies. It is more common in the dog than the cat. The theory behind this prevalence is that dogs secrete higher concentrations of the metabolites of tryptophan, a proposed carcinogen, than cats. Most tumors of the bladder are malignant, and the most common types include transitional cell carcinoma, squamous cell carcinoma, and adenocarcinomas. Bladder tumors usually affect older animals (mean age 10 years), with the exception of rhabdomyosarcomas that usually affect young animals. Etiology of bladder cancer in dogs and cats is unknown. However, risk of bladder cancer was found to be significantly increased in dogs exposed to two or more applications of topical insecticide commonly used for fleas and ticks, and also by obese body condition. It has been proposed that body fat acts as a storage depot for chemicals from insecticide dips resulting in gradual metabolism and excretion of the chemicals and prolonged exposure of the urothelium to the potential carcinogens. Cigarette smoking is associated with increased incidence of bladder cancer in people, and thus it is possible that second hand cigarette smoke exposure in animals living in smoking households may also play a part in the causation of bladder tumors. Cyclophosphamide has been incriminated in the development of TCC of the urinary bladder in dogs and humans. There is also a significant breed predisposition among dogs, with Scottish Terriers having an 18-fold increased risk compared to mixed breeds for TCC development. Other breeds with higher risk include the Beagle, Shetland Sheepdog, Wire Hair Fox Terrier, And West Highland White Terrier. This breed predisposition may be associated with differences in activation or detoxification pathways for specific carcinogens, although precise molecular pathways have yet to be identified. CLINICAL SIGNS Clinical signs most often associated with bladder tumors include hematuria, pollakiuria, and stranguria. Other clinical signs include polyuria, polydipsia, urinary incontinence, urinary obstruction, abdominal pain, tenesmus, ribbon-like stool, and lethargy. Physical exam findings may reveal caudal abdominal mass, prostatomegaly, bladder distention or obstruction, abdominal pain, weakness, and lymphadenomegaly. Most often, routine blood work and physical examination are normal and the bladder mass cannot be detected by abdominal palpation. DIAGNOSIS Urinalysis is often consistent with a bacterial cystitis (bacteruria, pyuria, hematuria, and proteinuria). Neoplastic cells can be identified in the urine se- 90
58° Congresso Nazionale SCIVAC • Milano, 7-9 Marzo 2008 • Oncologia veterinaria - Alle soglie del III Millennio diment. There can be over interpretation of the criteria of malignancy in cells in the urine sediment as inflammation by itself can cause changes that closely mimic malignancy. Flow cytometry may be more sensitive in the evaluation of bladder cells in urine. Its use to identify cancer cells may be valuable in the recognition of malignant cells as well as a sensitive indicator of response to therapy. Secondary bacterial infection is also common and there is often reported an initial response to antibiotic therapy followed by a return of the clinical signs when antibiotic therapy ceases. A new urine-based diagnostic test is commercially available in the United States for screening for bladder cancer in the dog. This test is referred to as the VBTA test and detects an oncofetal antigen released by tumors into the urine of affected dogs. While this test is highly sensitive, it is very non-specific. The test had an overall sensitivity of 90% and a specificity of 78% in one study of 19 healthy control dogs, 20 dogs with TCC, and 26 dogs with non-neoplastic urinary disease. Any cause of hematuria can result in a false positive finding with this assay. For this reason, we are not commonly using the test and suggest that all positive tests in a screening setting be validated by careful cytologic, biopsy, and imaging studies. Radiography is probably the most valuable tool in the diagnosis of bladder tumors. Plain radiographs of the abdomen usually do not provide the diagnosis, however, positive and negative contrast cystograms readily identify mucosal irregularities, filling defects, and masses. Radiographs should also be examined for calcification of the bladder wall, sublumbar lymph node enlargement, prostatomegaly, caudal abdominal mass, bladder displacement, and periosteal reaction along the lumbar vertebrae or pelvis. Ultrasound can be used as a diagnostic tool to look for bladder masses as well as evaluate the kidneys, ureters, and sublumbar lymph nodes for metastatic disease. Further, masses within the bladder can be easily measured at each ultrasound and used to evaluate response to treatment. Intraveneous urograms are often not necessary to diagnose bladder masses unless urethral obstruction prevents urinary catheter passage. It is estimated that 20% of dogs with TCC have metastasis at the time of diagnosis, although this metastasis may be confined to sublumbar lymph nodes. Thoracic radiographs to detect evidence of lung metastasis should be performed at the time of diagnosis. Most typical patterns of pulmonary metastasis seen with TCC are interstitial nodular and diffuse interstitial patterns. While much can be gained from performing the above diagnostic tests, the final diagnostic step should include biopsy. Biopsy can be obtained by cystoscopy, traumatic catheterization, or cystotomy via laparotomy. 91
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58Â° Congresso Nazionale SCIVAC: Oncologia veterinaria

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