Pathology of canine bladder and urethral cancer and correlation with tumour progression and survival.

Biopsy and necropsy specimens, comprising 107 primary carcinomas and three mesenchymal tumours, were reviewed from 110 dogs with cancer of the bladder, urethra, or both. Histological classifications developed for the assessment of human bladder cancer were found to be readily applicable to the dog. These classifications are based on histological features, including the pattern of growth, the cell type, the grade of transitional tumour and the depth of invasion of the bladder wall. Features associated with localized disease in canine transitional cell carcinoma included papillary architecture, "in-situ" tumour, low tumour grade and a strong peritumoral lymphoid cell reaction. Features of tumours with metastasis included infiltrating and non-papillary architecture, increasing tumour grade, depth of invasion, vascular invasion and presence of peritumoral fibrosing reaction. Wide variability was found within single tissue samples, indicating that multiple sample sites are necessary for the adequate characterization of a given lesion. Statistically significant correlations were found between: tumour grade and depth of invasion (P < 0.0001); tumour grade and presence of metastases (P < 0.029); and peritumoral desmoplasia and metastases (P < 0.029). It was concluded that canine bladder cancer could be classified for the purpose of clinical management with a modified World Health Organization system as developed for human tumours.