Naturally occurring and braken-fern-induced bovine urinary bladder tumors. Clinical and morphological characteristics.

Clinical and morphological characteristics of 139 naturally occurring and 20 braken-fern-induced urinary bladder tumors of cows were studied. Hematuria was prominent and occurred as early as 60 days after braken fern feeding began. Anemia and changes in leukocytes were late manifestations. Papillomas appeared as early as 1 year, whereas invasive carcinomas did not develop until 2.6 years after initiation of feeding. Twenty of 30 cows fed braken fern developed bladder tumors within 5.3 years. None of eight untreated control cows that lived 4 years or six that lived 10 years developed neoplasms. Naturally occurring and fern-induced bladder tumors were epithelial (35%) or mixed epithelial and stromal (55%). Papillomas occurred in 24% and carcinomas in 61% of naturally occurring cases, whereas there were papillomas (40%) and carcinomas (50%) in fern-fed cows. Naturally occurring tumors were metastatic to regional lymph nodes and lung. No metastases were detected in fern-fed cows.