Skeletal Metastasis of Canine Urothelial Carcinoma: Pathologic and Computed Tomographic Features.

Invasive urothelial (transitional cell) carcinoma (UC) is the most common cancer in the canine urinary tract. Prolonged survival of dogs with UC due to better management of the primary tumor and prevention of urethral obstruction might have contributed to an apparent increase in distant metastasis. Metastasis to bone is particularly concerning because the ensuing pain often leads to euthanasia; however, little is known of the frequency, site, or nature of UC skeletal metastasis. In a retrospective analysis, 17 (9%) of 188 canine UC cases had histologically confirmed skeletal metastasis, mainly to the vertebrae. In a prospective analysis of 21 dogs with UC that underwent total body computed tomography (CT) at euthanasia followed by a standardized pathologic examination, skeletal lesions detected on CT were suspected to be metastatic in 4 dogs and were confirmed as metastatic UC histologically in 3 (14%) dogs. In all 3 cases, skeletal metastasis had been suspected based on history and physical examination; however, 1 dog had additional CT-detected skeletal metastases in a clinically unsuspected location, and 2 dogs had histologically confirmed skeletal metastases that corresponded to nonspecific osseous lesions on CT. These findings suggest that total body CT could be helpful in detecting skeletal metastasis as a cause of bone pain in dogs with UC as well as in identifying clinically "silent" sites of skeletal metastasis.