Uncommon skeletal metastasis secondary to transitional cell carcinoma

BACKGROUND: Canine transitional cell carcinoma (TCC) is the most common type of malignant tumor of the urinary system. This tumor rarely metastasizes to bones, and dogs most commonly present with lower urinary tract signs. CASE DESCRIPTION: An 8-year-old female spayed beagle presented with unilateral front-limb lameness in which pain was localized to the shoulder joint. Surgical bone biopsy following abnormal radiographic lesions noted in the scapula was consistent with metastatic carcinoma of unknown origin. Abdominal ultrasound revealed a mass in the trigone region of the urinary bladder, which was cytologically confirmed to be a transitional cell carcinoma. Amputation was elected due to severity of the limb pain, and chemotherapy for the TCC was scheduled to follow after healing from surgery was complete. At the 2-week recheck for commencement of chemotherapy, the patient was anemic and a pathologic fracture was found on the L5 vertebra. Due to poor prognosis, the owner elected for humane euthanasia. CONCLUSION: This case report documents the clinical and pathological findings of a dog where metastasis to a rarely documented distant bone site secondary to TCC was diagnosed before the primary tumor. The unusual sequence of events described in this case report is a reminder to always consider all the possible differential diagnoses, as that may influence our recommendation on diagnostics and treatment.