Case 180810 -3

Twelve-year-old, male, castrated, Scottish terrier dog.

Approximately 4 months prior to biopsy, the patient began having urinary accidents in the home. About 2 months after that, the accidents increased in frequency, and the patient was brought to the referring veterinarian. An abdominal ultrasound was performed at that time, and revealed a mass in the lateral wall of the urinary bladder. Blood was submitted for genetic testing and the patient was found to be positive for the BRAF mutation. One month later, the patient presented to Oncology service for evaluation of possible metastasis and surgical excision of the mass. Abdominal ultrasound and thoracic radiographs did not reveal any overt metastasis, and surgery was performed to excise the mass.

One small jar of formalin was received, labeled "bladder mass". The jar contained a 2 cm diameter piece of tissue that was expanded by a 1.2 x 1.5 x 1 cm soft, yellow to tan, irregularly marginated mass. Cross section through the mass revealed a smooth, uniformly tan mass extending from the wall of the bladder.

One section of urinary bladder mass is examined in which the mucosa is expanded by a polypoid, densely cellular, well-demarcated, unencapsulated mass. The mass is composed of polygonal epithelial cells arranged in cords and trabeculae within a fine fibrovascular stroma. Neoplastic cells often invade through the basement membrane, forming small nests and islands within the lamina propria. Neoplastic cells contain a moderate to abundant amount of finely vesiculated eosinophilic cytoplasm. Occasionally there are large, clear cytoplasmic vacuoles. Nuclei are round to ovoid and have coarsely stippled chromatin and 1 to 3 prominent nucleoli. Anisocytosis and anisokaryosis are moderate, and occasionally cells contain two or three nuclei. Mitoses are 105 per ten 400x field, including frequent bizarre mitoses. Neoplastic cells occasionally fill vessels (of lymphatic origin). Throughout the mass there is frequently individual cell necrosis. The surface of the mass is overlain with pale eosinophilic fibrillar material, erythrocytes, and streaming nuclear debris (interpreted as hemorrhage). Small numbers of lymphocytes and plasma cells are scattered throughout the mass and lamina propria, and occasionally forming larger nodular aggregates within the submucosa. The submucosa is also expanded by clear space (edema).

No special stains.

Urinary bladder mass: Urothelial carcinoma (syn. Transitional cell carcinoma) with lymphatic invasion.

Urinary bladder: Mild, regionally extensive, chronic, lymphoplasmacytic cystitis

The histomorphology of the urinary bladder mass is consistent with a urothelial carcinoma (transitional cell carcinoma), and is classified as "high grade" based on invasion into the subjacent lamina propria, invasion into regional lymphatic vessels, and a high mitotic count (105 per ten 400x fields). Although examined margins are free of neoplastic cells, the lymphatic invasion raises concern for metastasis. In addition, it is mentioned in the literature that these tumors can slough and implant at other sites within the bladder mucosa, and along the excision site; therefore local recurrence is possible.

The patient developed hind limb weakness before staging and chemotherapy was performed. Over the next several weeks, the weakness progressed to paraplegia and he became painful. He presented to emergency where radiographs showed a pathologic fracture of L3 vertebrae. The cause was presumed metastatic disease, and the patient was euthanized.

Meuten, DJ. Tumors in Domestic Animals. Ames, Iowa: John Wiley & Sons Inc., 2017.

Case contributor: Drs. Melissa Roy and Brian Murphy. Conference presenters: Drs. Melissa Roy and Kevin Keel