Abstract
A 3-year-old spayed female English Springer Spaniel was presented twice 4 months apart for investigation of hematuria and pollakiuria without urinary tract infection. Both ultrasound examinations identified a stable craniodorsal bladder wall thickening. The first cystoscopic biopsy samples indicated lymphoplasmacytic cystitis and the second polypoid cystitis. The dog was represented 8 months later for recurrent clinical signs despite medical management. Although the ultrasound examination showed stable disease, repeat cystoscopic biopsy identified transitional cell carcinoma (TCC), confirmed on tissue removed by partial cystectomy. No BRAF mutation was ever detected in urine or tissue samples. To our knowledge, this case represents the first report of presumptive malignant transformation of polypoid cystitis into an apical TCC in a dog. Dogs with polypoid cystitis should be followed closely and surgical management considered if rapid resolution is not achieved with medical management.