Spontaneous urinary bladder tumors in DA/Han rats: a feasible model of human bladder cancer.

In a life-span study of virgin DA/Han inbred rats, 53.9% of the males and 14.4% of the females developed spontaneous urinary bladder tumors. A peak incidence was noted between the ages of 25 and 30 months. With the exception of 1 leiomyosarcoma, all neoplasms were of epithelial origin. After the papilloma, the majority of tumors were classified as transitional cell carcinoma of the papillary, solid, or mixed type. Less frequent were unclassified microcarcinoma, squamous cell, adenoid, and undifferentiated carcinomas. A sexual difference was found for almost every tumor type. Of the rats bearing tumors, 3.5% of the males and 64.4% of the females also were affected with urinary bladder stones. Squamous cell and glandular metaplasias of the tumors commonly were observed, and invasive growth into the bladder wall occurred frequently in less-differentiated tumors. Metastases were rare. The DA/Han rat strain is discussed as a suitable animal model for human urinary bladder cancer.