Complete ultrasonographic response of a primary bladder lesion followed by extra-vesical progression after lapatinib–piroxicam rescue therapy in a dog with urothelial carcinoma

Urothelial carcinoma is an aggressive malignancy of the canine lower urinary tract that is frequently associated with urethral obstruction and limited therapeutic options after chemotherapy failure. We describe the clinical course and serial ultrasonographic responses to lapatinib–piroxicam rescue therapy in a 15-year-old spayed female French Bulldog with trigonal urothelial carcinoma, following an initial partial response to vinblastine and subsequent disease progression. Initial treatment with vinblastine, administered every two weeks for a total of eight doses, achieved partial response. However, the recurrence of hematuria and complete urethral obstruction prompted second-line treatment. Combination therapy with lapatinib (25 mg/kg/day) and piroxicam (0.3 mg/kg/day) induced rapid tumor regression, with a partial response documented by ultrasonography on Day 14 and a complete response of the primary urinary bladder target lesion on Day 30 according to cRECIST criteria. Adverse events observed during treatment included increased alkaline phosphatase activity, anorexia, vomiting, and diarrhea. Although the primary urinary bladder target lesion remained in complete response, a new intra-abdominal mass cytologically consistent with urothelial carcinoma was detected on Day 60, constituting overall progressive disease according to cRECIST, and the patient died two days later. This case demonstrates that lapatinib–piroxicam rescue therapy was associated with a rapid complete ultrasonographic response of the primary urinary bladder lesion following an initial partial response to vinblastine and subsequent disease progression; however, this local response was followed shortly thereafter by extravesical disease progression. Serial ultrasonographic assessment according to cRECIST provided an objective and practical method for monitoring treatment response throughout the course of therapy.