Lower urinary tract tumors

Introduction

Lower urinary tract tumors of the urinary bladder and urethra accounts for approximately 1-2% of reported malignancies in dogs. The most common tumor of the lower urinary tract is transitional cell carcinoma (TCC), but other differentials such as squamous cell carcinoma, undifferentiated carcinoma, adenocarcinoma, rhabdomyosarcoma, fibroma, other mesenchymal neoplasia and metastatic neoplasia exist. Unfortunately, most TCC’s in veterinary medicine are aggressive and invasive intermediate to high-grade papillary tumors. The etiology of bladder cancer, like most cancers across species is multifactorial. Risk factors identified to date include gender (female predisposition), breed (Scotties, Shelties, Beagles, Wirehaired Fox Terriers, Westies), cyclophosphamide administration, obesity and exposure to insecticides and/or herbicides. In a case control study of 166 Scottish Terriers, exposure to herbicides and/or insecticides through household lawn & garden chemicals was compared between Scotties with TCC vs. controls. There was no increased risk for TCC in lawns treated with insecticides alone, whereas the risk was statistically increased with herbicide use alone or with concomitant herbicide/ insecticide use. Earlier case control studies have found an increased risk for topical application of flea and tick dips, but newer spot-on products were not associated with an increased risk of TCC.

The most common location for lower urinary tract TCC’s is the trigone region. Due to this anatomical location, partial or complete urinary obstruction can be common sequelae. Prostatic involvement in the male dog is common, and it is more common for prostatic tumors to be prostatic urethral TCC than true prostatic adenocarcinoma. On presentation, approximately 15% of dogs with TCC will have local lymph node metastasis and/or distant metastasis, whereas upon death, approximately 50% of dogs with TCC will have distant metastasis. The WHO staging TNM-based system has tumor designations from Tis (carcinoma in situ) through T3 (invasion of neighboring organs) with approximately 75% of canine TCC’s are T2 (invasion of bladder wall) and 20-25% are T3. These data further strongly suggest these are locally aggressive tumors with significant metastatic potential.

There are relatively scant data on urinary bladder TCC’s in cats. Wilson et al reported on the clinical signs, treatments and outcomes of 20 cats with urinary bladder TCC. When compared to dogs, cats appear to have a reduced number of trigonal lesions, whereas most other aspects concerning this disease are similar between dogs and cats (i.e. clinical signs, metastatic propensity, response to various therapies, etc.).

Diagnosis & staging

The most common clinical signs for dogs and/or cats with lower urinary tract tumors are hematuria, pollakiuria, dysuria and occasionally lameness due to hypertrophic osteopathy and/or bone metastasis. It is quite common for the urinary tract signs to temporarily resolve after antibiotic therapy. When a lower urinary tract tumor is suspected the minimum database should include a thorough physical exam, rectal exam (urethral thickening, mass effect and/or lymph node metastasis), CBC/Chem/UA (not cystocentesis-derived due to the chance for tumor tract seeding), urine culture, cystosonography or contrast cystography and 3 view chest radiographs. This author has found with an accomplished ultrasonographer, the utility of cystosonography is higher than with contrast cystography, especially when the bladder is not distended with urine and/or infused saline. Similarly, the ultrasound then allows for a complete examination of the abdomen looking for lymph node enlargement and/ or other problems.

Histopathologic confirmation is the gold standard for diagnosis of lower urinary tract tumors, including TCC. This is because inflammation-reactive epithelial cells are commonly indistinguishable from neoplastic cells on cytologic examination. Similarly, false positive results can be common with urine antigen tests when the urine is hematuric. Furthermore, a urethral and/or bladder mass on workup can be caused by granulomatous disease, other malignant tumors or a benign tumor, so the presence of a mass does not equate to the diagnosis of TCC. Methodologies for obtaining tissue for histopathologic diagnosis include cystoscopy, cystotomy and less reliably through traumatic catheterization. For those patients with a specific lameness not explained through common neurologic and/or orthopedic diseases, X-rays of the problematic area and/or nuclear scintigraphy (“bone scan”) should be seriously considered.

[...]