Histogenesis of urinary bladder cancer induced in rats by bracken fern.

Histologic examination of the urinary bladders of albino rats fed bracken fern (Pteris aqulinum) showed epithelial hyperplasia in all test animals after 3 weeks of feeding and nuclear abnormalities at 4 to 6 weeks. Epithelial tumors were present in animals surviving more than 12 weeks, and invasion of subepithelial tissue occurred in animals sacrificed after this time. Carcinoma in situ, comparable to that in man, was not observed before invasive carcinoma, but was noted later in the surface epithelium adjacent to invasive carcinoma. Transitional cell carcinomas originated from hyperplastic epithelium, squamous cell carcinomas from metaplastic squamous epithelium, and papillary carcinomas from papillomas. Papillomas were preceded by epithelial hyperplasia. The results suggest that hyperplasia precedes bladder carcinoma in rats fed bracken fern.